Once you are on Agency or Enterprise plan you can start adding your colleagues to your team. For that find the "Team" item under your account menu.
If you are an administrator you can start adding your team members.
There are three roles: Administrator, Developer, and Read-only. The main difference is that an Administrator can manage team members (can add/remove others) but a Developer can't and the users having Read-only access can only see the results, but can't start jobs nor change any settings.
Below is how the Team page looks like.
Invitations. Switch between teams
Once you have invited someone to the team they will have a message at the top of the screen to accept the invitation.
After accepting the invitation person can switch between the invited team and their own from the header.