Before anything I want to thank you for considering contributing to this project.
Packages are not stored in this repo, and in the time that I'm writing this, they are stored in the official JAPM repo
If you want to create a package you need to follow the repos you want to post them into contributing guidelines.
There's many ways you can contribute to the project: creating issues, reporting bugs, creating pull requests, commenting about other contributions and generating discussions around them.
Before creating a pull request make sure that your code compiles and JAPM works as intended.