UE4 and Github, how can a collaborator save things to the repository?

Hello smart people I need some help. Me and a few of my friends are trying to make a fun little game. We all made a Github account and I made a repository, connected my UE4 project with source control to it and invited all of my friends but I dont know how they can connect to my repository with source control so they can save stuff aswell. Please let us know if you know how this works, we need help. Thank you