Cut one of your 10-foot PVC pipes into two 40-inch pieces and two 20-inch pieces. The 40-inch pipes will serve as the goalposts, while the 20-inch pieces will lie flat on the ground perpendicular to the posts.
Cut the other 10-foot pipe into two 51-inch pieces. These pieces will connect each post together, one along the ground in the back and one across the top as the crossbar. The remaining 18-inch piece is leftover and is not needed for the goal.
Use elbow connectors to connect the correct pieces together. One elbow connects each 40-inch goal post to a 20-inch bottom side base. One elbow connects each 40-inch goal post to the 51-inch crossbar. One elbow connects each 20-inch bottom side base to the 51-inch pipe that serves as the back of the goal and lies on the ground. The PVC pipes should easily slot into place inside the connectors.
Slip the hockey net over the frame of the goal. Tuck the net in under the PVC pipe on the ground. If necessary, use small ties to keep the net on the frame. Set up the goal in the proper location.