There are more details at the official contribution guidelines.
In a nutshell:
- Fork the repo
- Clone the repo
- Track changes
- Create a new branch on your fork
- Change and TEST your code
- Commit and push
- Create a pull request
- Wait for a review
- Fix anything the review brought up
- Celebrate when the code gets merged!
If you have questions, see the MongoDB Community Forum posts with the O-FISH tag or create a new post.