The word "finna" is a colloquial contraction used primarily in African American Vernacular English (AAVE). It means "going to" or "about to," and it's often used to express a future intention or plan. For example, when someone says, "I'm finna go to the store," they mean that they are about to go to the store soon.
"Finna" is derived from the phrase "fixing to," which is used in Southern American English. The phrase has evolved over time and has become particularly prominent in African American Vernacular English.