Open the Project Settings menu of your project. You can find this option as shown in the image below.

In the Project Settings menu, select Team:

In the team page it will be needed to:

1. Fill the e-mail address of a team member over here;
2. Give the team members view access or admin access;
3. Click on Send Invite to send an invitation in their inbox.

Once the invitation is accepted, the team member will be part of the project.

View access: Team members with this level of access can look at everything in the project but cannot change anything. This is great when you want someone to keep an eye on performance without them changing anything

Admin access: Team members with this level of access can view and change anything they want.

It is also possible to change the permissions or remove the access to the project of an existing team member by opening the menu at the right of its name and clicking either Remove or Make admin:

That's it!

It is possible to add as many team members of the project as needed.