The reduced form "gonna" should not be used in compositions. "Going to" is the equivalent form. It is informal speech.

"gonna" (this is spelled with two n's) is a slang form for "going" as in "I'm gonna tell you" (I am going to tell you). This should not be used in writing, unless you are quoting sombody who is taking.

As a native English speaker I hate when other native speakers use "gonna" in their speech. It should never ever be used in writing. The other slang terms that should never be used at below. - Gonna - Wanna - Gotta - Dunno - Uh Oh - Uh-Huh - Yup Many others...

Gonna (informal) = going to wanna = want to gotta = got to donna = dunno = don't know ....