A Sedevacantist.
Google for it.
Can someone explain to me the difference between Christianity and Catholicism?
There is no difference. Catholicism is one of the version of Christianity, like Orthodoxy, Luteranism, Calvinism, Baptism and many others. They vary in some aspects but all are considered as Christianity.
Yechovas (sp?) and Mormons don't count as Christianity, although they've developed from it (for the most part).
-Catholics pray to Jesus' mother Mary.
No, they don't. Mary isn't a god in any of the Christian sects (that would be polytheism).
The cult of Virgin Mary in Roman Catholicism became so overdeveloped in 20th century (like the dogma of Assumption of Mary). As a Sedevacantist (yeah!), I don't agree with those "new" additions.
-Catholics oppose the use of condoms (not ALL Christians oppose this)
-Catholics oppose gay marriage and female bishops (not ALL Christians oppose this)
Ugly stereotypes. Those are not just Catholic things.
As for condoms, it's actually a matter of non-wedding sex, rather than condoms themselves. There is no version of Christianity which allows to have sex with anyone (maybe except those libertarian sects created in America in 20th and 21st centuries).
As for homosexual marriages, it's overwhelming majority that opposes them. The most gay-tolerant denominations are actually those libertarian Neo-Protestant American sects like "The United Church of Christ's Awesomest Dudes" (a hypothetical, demonstrative name), who even hire gay men as priests. Such sects break the most fundamental rules of Christianity (it's not only about gay marriages but also many, many other things) and many refuse them as Christianity.
Just some information. Hope it helped.