The Brief: Finna means gonna or "going to".

DEEP DIVE
It is short for “fixing to.”
Crew I’m finna slay, the street life I crave -Kendrick Lamar, “m.A.A.d. City”
Iβm finna go buy a lambo.
— RUN IT UP/ACCOUNTANT OUT NOWπ₯π₯ (@PontiacMadeDDG) September 13, 2018
This how my 7+ boutta start acting now that they finna drop the new iPhone pic.twitter.com/VI2v0EcBgL
— draaaaakee?? (@kashmirVIII) September 12, 2018