If you are working with others you probably don’t want to share your code publically.
On Github.com in the repository, click Settings
Click Manage Access
Click Invite a collaborator
Enter the username or email of the person to add.
Click Add … to this repository
The user us now invited.
You can add additional users through Invite a collaborator
The user you invited will have to go to their email and accept the invitation.
Once they have the pending invite will disappear and they will have access to your repository.