I'm good at

Again, 'I'm' is used here as 'I am.' 'Good at' informs someone what you excel at and are comfortable doing.

Here are some examples:

"I'm good at drawing."

"I'm good at video games."

"I'm good at swimming."

"I'm good at driving."

"I'm good at reading."

"I'm good at sports."

"I'm good at writing."

"I'm good at math."

"I'm good at dancing."

"I'm good at chess."

I'm getting

When combining the words 'I am' and 'getting' you are telling someone 'you' are gaining possession, being affected by or have plans to seek out and obtain a particular thing.

Here are some examples:

"I'm getting better."

"I'm getting ready for bed."

"I'm getting a tooth ache."

"I'm getting a cold."

"I'm getting married."

"I'm getting tired."

"I'm getting good at reading."

"I'm getting a new car."

"I'm getting a job."

"I'm getting a puppy." 

I'm gonna + (verb)

The word 'gonna' is incorrect grammatically. The equivalent in proper grammar would be 'going to.' When using the word 'gonna' you are telling someone what you are planning to do at that moment or in the near future.

Here are some examples:

"I'm gonna have some coffee."

"I'm gonna go to work."

"I'm gonna eat some cake."

"I'm gonna send out my resume."

"I'm gonna run a marathon."

"I'm gonna ask her out for dinner."

"I'm gonna stop smoking."

"I'm gonna help my friends."

"I'm gonna take swim lessons."

"I'm gonna read a book."