You can add (and remove) team members in your account settings:
Please click on the blue button in the upper right corner.
Fill in all details and click
invite(for security reasons we recommend using the same domain-ending for e-mail addresses).
The invited person will receive an e-mail to accept your invitation (make sure your team member also checks the spam file).
Depending on your plan, you will experience limitations in seats.
Basic Plan: 1 seat
Advanced Plan: 5 seats
Enterprise Plan: unlimited seats