Actually you can find this all in wikipedia, but: The main branches of christianity are Catholicism, Eastern Orthodoxy and Protenstantism. Catholic Church can be divided into Roman Catholic, Old Catholic and Independed Cathlic. If you need more details you can find it on Wikipedia.

Roman Catholic is a "type" of Catholic that uses the "Latin rite" and is in union with Papal authority (the Pope) and the teachings of the Catholic Church. There are other Catholic "rites" which are in union with the Pope (e.g. Alexandrian, Armenian, Byzantine, East Syrian, and West Syrian) There are also other churches that claim to be "Catholic" and use a similar worship styles but are not in union with the Pope and therefore not technically "Catholic." At least in America, if someone just says they are "Catholic" they usually mean "Roman Catholic."

I am not sure about what I am going to say. However as far as I know. When you said Christian it is a term very big and it has many denominations who belong to Christianism. Roman catholic belongs to Christianism and It is the biggest and widely spread throughout the world. Its headquarters is in Rome (specifically in Vatican city which is a very small country) I don´t know if there are a denomination who is called Catholic. Supposedly a person who is Christian follow Jesus Christ's teachings and what in the bible is. There are many denominations around the world which belongs to the Christianism but many are different from one another. I think that the 2 biggest are Roman Catholics and Protestant Christians. The Roman Catholics that I know don´t read the bible, and they only follow what they have seen from their parents and ancestors. The have many statues and they burn candles to them. They believe in saints, in Mary, etc. The Protestant Christian usually read the bible every day and follow what It is inside the bible. They don´t have any statues and they don´t burn candles to them, they don´t believe in saints and In Mary. They only believe in God (the father, the Son, the holy spirit which are only one and this is a mystery difficult to understand for an atheist).

Christian is a more general term for anyone who believes Jesus Christ to be Lord and Savior and follows His teachings from the Bible. If you are a "Christian" but not a "Catholic" then you are called a "Protestant." There are thousands of types of Protestants (e.g. Baptist, Episcopal, Lutheran, Greek Orthodox, non-denominational etc...) Some Christians belong to a specific church and others do not. The common beliefs though are that there is one God and three persons (Father, Son, Holy Spirit) in one God. (The trinity) They believe the Bible is the true and inspired Word of God. They believe Jesus Christ (the Son) was born as a man and came to redeem and save all creation. Because mankind had sinned (chose to turn away from/reject God) they would have to die and it would be an eternal death (separation from God) unless God intervened to redeem mankind. So Jesus Christ took upon himself the punishment of all mankind and suffered and died for our sins and then rose again from the dead and ascended into Heaven, thus opening the Heavenly gates for all believers to enter into eternal life. Where Christians start to disagree from one group to another (or person to person) is about what (if anything) must be done or believed in order to get to Heaven. They disagree on how to live and many social teachings. They disagree about whether the Bible is literal or if there are parts that are not meant to be taken word-for-word. This is getting really long...if you have more questions feel free to contact me. :)

There are other groups of believers who would not want to be categorized as simply Protestants. These include but are not limited to Unitarians and nondenominational Christians. There are also those in the church often referred to simply as LDS. This group possibly also includes Jehovah's Witnesses and some Jewish congregations who revere Jesus Christ.