You can do this from the "My Workspace" section
Once you are in the "My Workspace" section, enter the email address(s) of the user whom you would like to invite to your team.
Then, click on the "Invite People" button.
The invite will reach the invitee's email, from where they can click on the "Join Team" button to join your team.
Note: If you have a paid plan in your account and want to invite a team member, you will be asked to pay when you send the invite.