Contribute: Go to projects which interest you. Add a note or a sketch. Your contribution will make your name tag appear in the project, and it will appear in the EVENTS board of the project founder.
Invite: Go to the homepage of penccil members. On their homepage, click the name. Choose the project you want to invite this member to and click send. Invitations will be sent to the Inbox of the invitee and forwarded to their email.