First, you must have at least 1 outpost. go to that outpost, click on it, an click the "invite friends to move button". After you clicked it, a send messagew box will pop up. Send that invite to your friend, and if your friend accept, his yaqrd will be at your outpost's position. Please note that you'll have to sarcrifice 1 outpost for your friend to move near you. You can also revoke the invite at any time.