Loosen the connection between the axle of the bike's back wheel and the frame of the bike. Loose the screw on the end of the axle by turning it counterclockwise with an adjustable wrench. If you have a quick release wheel, lift the arm of the quick release away from the wheel of the bike. Don't take the wheel off of the bike.
Connect the front-most part of the trailer to the back axle of the bike. Slide the bracket on the front of the arm of the trailer over the back axle of the bike.
Secure the back wheel of the bike to the frame. Tighten the bolt on the end of the axle that you previously loosened. If you have a quick release wheel, press the arm of the quick release device toward the wheel.
Attach the safety strap of the trailer to the bike. Locate the strap that is on the arm of the trailer. Wrap this strap around the frame of the bike and back toward the trailer. Fasten the strap to the trailer. This is typically a snap connection. Press the snap on the strap to the corresponding snap button piece on the trailer.