Sponsored maintainers are people who maintain packages in the Debian archive without having any upload rights. The packages are uploaded by a sponsor.
After a while, a sponsored maintainer can become a Debian Maintainer.
Anyone can create a package for Debian on their computer.
if you want to help Debian you can become a sponsored maintainer.
Becoming a sponsored maintainer
After these steps you will be a sponsored maintainer.
Step 1: Learn to create a package
You have read the Documentation.
You know that you can join a team.
You have found an interesting package
Step 2: find a sponsor
You have created an account on mentors.debian.net
You have uploaded your package on mentors.debian.net (read more)
You can use Salsa for your package.
A sponsor has helped you with it.
Once your package is in Debian, you are a maintainer who has been sponsored.