1. Make sure you are logged into the account to which you are team captain.
2. Once you are logged in hover your mouse/pointing device over your profile name and select "My Teams".
3. On the "My Teams" page you can select the team that you are looking for. Once selected, you will be given a page to which you can also manage your team as well as invite other people.
4. Once you select the team you would like to invite someone to scroll to the bottom (if applicable) and select the "Invite someone to register for this team".