Project members are users that have been assigned a role. Unlike Project Admins, which are added by the Platform Admin as part of the process of creating a Project, Project members are simply users that have been added to the Members tab.
To add members to a project, navigate to User Management | Members.
JFrog Platform New Navigation
If you use the new navigation, click Administration on the taskbar, and select User Management| Members. For more information on the new navigation, see JFrog Platform Navigation