Hi Luis
This section from SikhiWiki explains much (my comments in [brackets]):
Gurus direct Contribution
Guru Nanak and his successors attached a great deal of importance to langar and it became, in their hands, a potent means of social reform. The former gave it the central place in the dharamsala [early Gurdwara - Sikh place of worship] he established at Kartarpur at the end of his preaching tours. Guru Nanak, as did Guru Angad, toiled in the fields to provide for himself and for his family and to contribute his share to the common langar.
He had such of his disciples as could afford to set up dharamsalas and langars. Among them were 'Sajjan Thag, then lost to godly ways, and a wealthy nobleman, Malik Bhago, both of whom had converted to his message. Bhumia, formerly a dacoit, was asked by Guru Nanak to turn his kitchen into a langar in the name of God. A condition was laid upon Raja Shivnabh of Sangladip (Sri Lanka) that he open a langar before he could see him (Guru Nanak). The Raja, it is said, happily complied.
Guru Angad, Nanak II, further extended the scope of the institution. He helped with cooking and serving in the Langar at Khadoor Sahib. His wife,Mata Khivi, looked after the pilgrims and visitors with the utmost attention. Such was her dedication to work in the langar that it came to be known after her name as Mata Khivi ji ka Langar. Mata Khivi has the distinction of being mentioned in the Guru Granth Sahib by the bard Balvand who pays homage to her in his verses, in the SGGS. To quote the stanza:
SGGS Page 967 Shabad 3586 [page here]
"Guru Angad was proclaimed, and the True Creator confirmed it. Nanak merely changed his body; He still sits on the throne, with hundreds of branches reaching out. Standing at His door, His followers serve Him; by this service, their rust is scraped off. He is the Dervish - the Saint, at the door of His Lord and Master; He loves the True Name, and the Bani of the Guru's Word. Balwand says that Khivi, the Guru's wife, is a noble woman, who gives soothing, leafy shade to all. She distributes the bounty of the Guru's Langar; the kheer - the rice pudding and ghee, is like sweet ambrosia. The faces of the Guru's Sikhs are radiant and bright; the self-willed manmukhs are pale, like straw. The Master gave His approval, when Angad exerted Himself heroically. Such is the Husband of mother Khivi; He sustains the world. ((3))"
The Var by Satta and Balvand also applauds Guru Amar Das’s langar wherein “ghee and flour abounded.” In spite of rich variety of food served in his langar, Guru Amar Das ate a simple meal earned by the labour of his own hands. “What was received from the disciples was consumed the same day and nothing was saved for the morrow.” Contributing towards the Guru ka Langar became an established custom for the Sikhs. Partaking of food in Guru ka Langar was made a condition for disciples and visitors before they could see the Guru. Guru Amar Das’s injunction was: “pahile pangat pachhe sangat”—"first comes eating together, then meeting together.” Langar thus gave practical expression to the notion of equality.
At Goindwal, during the time of Guru Amar Das Ji a rule was instituted that anyone who wanted to have a meeting with the Guru (receive his Darshan) would have to eat food from the Langar. Even when the Emperor of India, Akbar came to see Guru Amar Das, he sat in pangat (where Langar is served) [pangat is where everyone sits on the floor in lines to eat - there is no distinction between high-class or low-class, no division by gender or caste] before meeting the Guru. From that time forward, at Goindwal, Langar was served 24 hours a day.
Bhai Jetha, who came into spiritual succession as Guru Ram Das, served food in Guru Amar Das’s langar, brought firewood from the forest and drew water from the well. By such deeds of devoted service, he gained enlightenment and became worthy of the confidence of Guru Amar Das. Langar served to train the disciples in seva [voluntary service] and to overcome class distinctions.
The institution of langar had become an integral part of the Sikh movement by now and, with the increase in its numbers, it gained further popularity and strength. With the development under Guru Ram Das and Guru Arjan of Amritsar as the central seat of the Sikh faith, the capacity of the local Guru ka Langar increased manifold. Sikhs came from far-off places to see their Guru and to lend a hand with the construction work. They were all served food in Guru ka Langar.
Bhai Manjh, was was attracted to Sikhism from a Muslim sect, engaged himself in serving the Guru's langar by fetching fuel wood from the nearby jungle. Once, due to inclement weather, he fell into a well whilst carrying wood on his head. On hearing this, the Guru Arjan Dev rushed to the well with necessary equipment. When the ropes were lowered, Bhai Manjh requested the Guru to draw out the fuel wood first, as he considered dry wood more essential than himself. It was done, and when Bhai Manjh was drawn out, the Guru embraced him in his wet clothes blessing him, "Manjh is the Guru's beloved. Whosoever keeps his company shall be redeemed."
Guru Hargobind and Guru Tegh Bahadur travelled extensively in north and northeast India. This led to the establishment of many new sangats. Each sangat meant an additional langar. In the reign of Guru Gobind Singh, the institution of langar acquired further significance. At Anandpur, the new seat of Sikhism, a num
ber of langars were in existence, each under the supervision of a devoted and pious Sikh. Food was available in these langars day and night.
And some more from the same SikhiWiki source, which gives more context to the equality side of things:
A Means of Social Reform
Community kitchens came into existence with the Sangat or holy fellowships of disciples which sprang up at many places in his time. Sikhs sat in pangat (literally a row) without distinctions of caste or status, to share a common meal prepared in the langar. Besides the kitchen where the food was cooked, langar stood for the victuals as well as for the hall where these were eaten. The disciples brought the offerings and contributed the labour of their hands to prepare and serve the food. The institution of Langar had thus demolished the long established caste barriers and gender prejudices of the time.
High caste Brahmins would eat from the hands of low caste Sudar and vice-versa. This practise, slowly overcame the century old established prejudices ingrained in the minds of common people of the land. Before the establishment of Langar, a Brahmin would not eat in the presence of a low caste person and was thought a bad omen if a low caste person was to enter a room where the high caste Brahmin was eating. The institution of Langar has contributed greatly in putting an end to these ancient social prejudices in the culture of Northern India.
Here's a lovely article about the langar hall at the Golden Temple (Harmandir Sahib) in Amritsar, India, which feeds 100,000 people daily:
In Pictures: Kitchen that feeds 100,000 daily - Al Jazeera English It have lots of awesome pictures
For me personally, I felt that helping in the langar really brought people together. The prayer hall is lovely, but it is formal, there is no talking in there, the focus is on the Shabad. When I was going to Gurdwara regularly, I would often try to get there early to help in the kitchen. It gives you something else to do whilst at the Gurdwara and you can talk freely with people. It feels good to serve people (and by extension, the divine within them). Everyone helps there; men, women, children, doing everything from stirring pots, buttering rotia, washing and drying dishes, folding the tea towels that have dried, cleaning up mess, washing pots, cutting salad, fixing things in there that break, serving food to people waiting, topping up empty food trays. It feels good to be among people working together for something other than pay.
I also remember when we had a politician come to the Gurdwara to give a speech to the community. He sat with us and ate langar afterwards, just like any of us. It was cool. It was human.
Anyone is welcome to attend Gurdwara and partake of the free langar. There does appear to be at least one Gurdwara in Brazil:
Shri Arjun Dev Sahib Gurdwara, Brazil - SikhiWiki, free Sikh encyclopedia.
I hope this information is useful to you.
Gurfateh