Nice and Simple :
Step 1 : Load up your Halo Wars 2 game
Step 2: Hit
for Campaign
Step 3 : Scroll Over to Co-Op hit
Step 4: Invite your Partner by hitting
, which opens the squad screen. Hit
again and send an invite to your partner.
Step 5 : Select the mission "The Signal" and pick any difficulty you would like
Step 6: Finish the mission and you will get your pop