Deal members are the people assigned to work on a deal. Both team and non-team members can be deal members, but only team members can add a new deal member.
Note: A task can only be assigned to a deal member. If you assign a task to a team member, they will automatically become a deal member if they weren't one already. You cannot assign a task to a non-team member until you manually add them as a deal member.
There are several places where new deal members can be added, but the process is the same for each. The main places are the Add Member button on the deal's Overview tab and the Invite New button on the deal's Members tab.
Upon clicking one of those buttons, you will see icons representing the people you can choose from. (Existing deal members will not be listed.) Hover over an icon to see the person's name. Alternatively, you can type a name in the search box. Click the icon for the people you'd like to add as deal members and a check mark will appear on their icons. When finished, select Close.
If the person you want to add isn't in this list, type their email address into the search box. This allows you to invite that person to collaborate with you in Activate as a non-team member.
Note: Even if the person you invite works for your organization, they will still be a non-team member. If they should be a team member, ask your admin to grant access.