Jesus personally taught 12 Apostles. Those apostles were given the responsibility to teach others the things that Christ taught them. But eventually these men died (all before the end of the 1st century ce) and other christians had to take over the teaching and preaching work.
But christianity is founded on the teachings of Christ as explained by first apostles. These teachings were written down in the New Testament christian greek scriptures. Initially all christians were teachers, there were no priests or bishops or popes. The experienced christian teachers were called 'elders' and they instructed the congregations in what the previous Apostles had taught. The christians were one unified group even though they lived in different areas.
Somewhere around 2/3rd century, some of these christians began to rise up and seize control of the congregations and things began to change...some made themselves leaders of the various congregations, they formed into churches with bishops and priests and a clergy class and then once these men were in charge of the churches they went even further by introducing new and different teachings which were not from the first apostles. This is how the church became so divided and its why there are over 30,000 different christian denominations today.
But the true basis of Christs teachings is still there in the greek scriptures and if a church only teaches what is in there, then they are teaching what Christ taught his apostles.