I guess the two main groups people usually think of are Catholic and Protestant; and yes, there are many differences between them. But there are other large groups like Evangelicals, Nondenominational, and Charismatics. And there are a lot of people who don't affiliate with any group. Christianity isn't about what group you affiliate with, but Who you affiliate with: the Lord Jesus.
More biblically: A crisis that threatened a Philippian jailer with death prompted him to ask Paul and Silas the most important question in life: “What must I do to be saved?” (ACTS 16:30) This question is most important, because—as sinful and mortal souls—we need saving from corruption, both moral and physical. We need saving from physical death if we value or enjoy life, and we need saving from immorality or evil-doing if it results in unhappy existence, especially after this lifetime.
The reply of Paul and Silas was this: “Believe in the Lord Jesus.” (ACTS 16:31) This is God's requirement for salvation (GRFS) in a nutshell. Jesus Himself expressed GRFS even more succinctly using three, four and five letter words: “Ask… seek… knock…” (MT 7:7). As Hebrews 11:6 states: “he [God] rewards those who earnestly seek him” (cf. IS 45:19).