To invite a user to a project, they’ll first need a user account created by their Organization Administrator.
Only Project Administrators from the project-owning organization can add project participants via the participant list. However, if they create custom user roles, they can also assign other users within their org with this ability.
Open your projects list, from Setup > List My Projects.
Hover over the row for your project, until the ellipsis menu (three dots icon) appears. Clicking this opens a list of options.
Select Project Participants.
Click Invite User to search for and invite the appropriate users.
Adding users
To find users, start entering their name (or by their company name) in the Users field. This automatically populates with possible users. Select the user you wish to invite. Do this for all the users you want to invite. You can also click Advanced Search to add users in bulk.
You can choose to send email notifications to users by selecting Send email notification in the Invite Users window. This opens the Message panel containing default invitation text, which you can edit as required.
When you’ve finished, click the Invite User button at the bottom of the view.
The users will now be added to the project and will receive an automatic email notification (if you chose to), outlining who has added them and to which project.