Open the door halfway and engage the washer to keep the door open. The washer is on the door closer rod behind the closer body.
Grab the body of the closer with one hand, and pull it slightly toward the handle side of the door to provide slack for the connecting pin. Hold the closer body in one hand while pulling the pin out with your free hand.
Pull the front of the closer up to the next hole on the mounting bracket and insert the pin through the bracket and closer. Open the door enough to release the washer and allow the storm door to close.
Find the adjusting screw on the end of the door closer body. Turn the screw a half-turn counterclockwise with a Phillips-head screwdriver if the storm door closes too slowly. Turn the screw a half-turn clockwise if the door closes too quickly.
Open the storm door and allow it close. Continue making adjustments until the door closes slowly enough to allow you to walk through and quickly enough that it latches shut behind you.