"Gonna" is lazy speech. Never write it. ;)

Gonna is the colloquial (slang) version of going to. You would never write gonna in a business or academic paper but it's said all the time. Also, gonna is used for cases that mean "will" or "about to", you would never use it to mean "going to" to mean actually leave and go to somewhere else. Correct: I'm gonna talk to him. Correct: I'm gonna go see a movie later. Correct: I'm going to his house. Wrong: I'm gonna his house.

Gonna: se usa entre los jóvenes y en algunas situaciones informales. Pero se ve muy feo (para mí) cuando alguien escribe "gonna" en un correo electrónico o en un texto. Going to: Es la manera correcta de decirlo; significan lo mismo pero con el siguiente matiz. Si alguien escribe "I'm gonna", se está identificando con un estrato socioeconómico concreto. O simplemente quiere lucirse menos formal. Suerte.