About collaboration in a personal repository
To collaborate with users in a repository that belongs to your personal account on GitHub.com, you can invite the users as collaborators.
If you want to grant more granular access to the repository, you can create a repository within an organization. For more information, see "Access permissions on GitHub."
If you're a member of an enterprise with managed users, you can only invite other members of your enterprise to collaborate with you. For more information, see "Types of GitHub accounts."
Private forks inherit the permissions structure of the upstream repository. This helps owners of private repositories maintain control over their code. For example, if the upstream repository is private and gives read/write access to a team, then the same team will have read/write access to any forks of the private upstream repository. Only team permissions (not individual permissions) are inherited by private forks.
Inviting a collaborator to a personal repository
You can send an invitation to collaborate in your repository directly to someone on GitHub.com, or to the person's email address
GitHub limits the number of people who can be invited to a repository within a 24-hour period. If you exceed this limit, either wait 24 hours or create an organization to collaborate with more people. For more information, see "Creating a new organization from scratch."
Ask for the username of the person you're inviting as a collaborator. If they don't have a username yet, they can sign up for GitHub. For more information, see "Signing up for a new GitHub account".
On GitHub.com, navigate to the main page of the repository.
Under your repository name, click Settings. If you cannot see the "Settings" tab, select the dropdown menu, then click Settings.
In the "Access" section of the sidebar, click Collaborators.
Click Add people.
In the search field, start typing the name of person you want to invite, then click a name in the list of matches.
Click Add NAME to REPOSITORY.
The user will receive an email inviting them to the repository. Once they accept your invitation, they will have collaborator access to your repository.