Trying to! It's like when people say "going to" it often sounds like "gonna".

It means "trying to." The nonstandard spelling is a way of showing how people actually pronounce the words "trying to" when they are speaking quickly or carelessly. The n-g-t combination requires quick tongue movements. "Trying to" easily becomes shortened to "Tryin' to," and then the vowel sound in "o" gets shortened to a little grunt or "schwa," "Tryin' tuh," and then finally the "i" sound and the "t" sound go a way, "try'n'uh" and thus "tryna." Song lyrics are not a good guide to standard English. The songwriter tries to be authentic and make a connection with the audience by using the informal language he uses, and that his audience uses, in everyday life. In books, these kinds of nonstandard spelling will usually be within quotation marks. The author is trying to indicate the real sounds and pronunciation used by a character.