I'm not a mason, although a member of my family was prominent in the craft, so I think I'm fairly impartial.
There are two main groups of masons.
1. The smaller, recognised by the Grand Orient Lodge in France and largely continental, accepts atheists.
2. The larger, recognised by the United Grand Lodge of England, requires members to have a belief in God. A copy of the local scriptures, whether the Bible, the Koran, or something else, is always present in the lodge. There's a famous print of George Washington and his fellow rebels attending a church service in their masonic regalia.
Obviously neither group are likely to be satanists!
The rites of masonry are not secret: you can find accounts of them in any good library. Membership tended to become secret in the last century because of political hostility from fascists and communists: up to the 19th century they had public parades, balls, and church services.
The goals of masonry are raising money for charity, fostering self-improvement, and plain sociability.