Need help registering to vote, party affiliation?

Well, I am am independent, and I just turned 18. I want to vote in the Republican primary, but I don't want to register as a Republican. I get mixed responses from Google, some people say if I register as an Independent I can't vote in any primary, others say I can vote in one primary... Which is true? If the first is true, can I register as a Republican now, and change my party later (if so, is there a time limit?)