When you send a invitation from create step 3, a mail is send to email specified.

Sample email

Hello [NAME],

'[TONTYNE OWNER NAME]' has invited You to be a team on project [TONTYNE TITLE] and by clicking on this link you accept the invite and after signing up or logging In. you become part of team on it and can edit some steps and help promote project

Accept Your invitation by click here [AGREE LINK].

Click on the Agree link. Now he/her is a part of your Tontyne.