Mari: Hi, Blake. What’s going on?
Blake: Not much.
Mari: Wanna come over for dinner tonight?
Blake: That’d be great!
Now let’s review the vocabulary
What’s going on? is an informal greeting in American English. It’s similar to “How’s it going?”
Not much is a response you can use when asked the question “What’s going on?”
Wanna is a shortened form in spoken English of the two words “want to.” “Wanna” is not used in written English unless it is very informal writing, such as text messaging.
Wanna come over is an informal invitation, used to ask someone to come to your house.