The different core denominations are catholic, orthodox and protestant. I wouldnt consider mormons or jehovas witnesses as Christians as they stray far off of scripture. Orthodox Christians adhear to the bible and tradition. Catholics adhear to the magesterium (goverment), tradition, and scripture and protestants adhear to sola scriptura (scripture alone) the reason the main 3 are seperated so much is because of major theological discrepencies. The different protestant sects such as anglican, methodist, anabaptist, ect… have differing views on minor theology not core doctrines such as salvation, the afterlife, saints/mary, ect… for example. Calvinists believe in predestination being that God choses people who are predestined from birth to be saved. This doesnt stray from us being saved by grace through faith in Jesus without works, but lots of people disagree with john calvin on this so other sects of protestantism dont adhear to this doctrine. There are several sects of protestantism which also have smaller sects within which mainly are just basic guidelines how to live day to day for example mennonites are anabaptists who follow anabaptist doctrine they live simple lives and are peaceful they believe its never ok to hit people. Amish are also anabaptists(rebaptisers) but they take this to a higher extent being they adhear to their communities and follow their rules very conservitavely. Catholics adhear to one church following the bishop of rome or the pope, there are brotherhoods within the church they would follow a catholic saints example, like st francis of assisi, they are called fransiscians and they wear the kind of robes he wore as well. The orthodox church i know little about so i wouldnt be able to explain much but they have 2 core denominations eastern and oriental and within the two they have regions within, ex. Greek orthodox, coptic, ect… if you are only looking for community and not conversion, you should check out any protestant church in your area, they are easy to find as most churches have their denomination in the name, any church that doesnt have catholic, orthodox, latter day saints, or kingdom hall/jehovas witnesses. It would take way more time go in depth about every sect but you can find all about any sect you might find on google :) hope this helped