Take your end panel and attach it to the wall side of your pantry cabinet. This will create more room for your pantry door to close. The panel needs to come out 20mm past the front of the cabinet to accommodate for the thickness of the door. Use two clamps, top and bottom, to hold the panel in place. Use your tape measure to make sure it's 20mm out. Then screw the panel to the side of your cabinet with your drill, using counter sink bits before each screw.
Before you slide the cabinet into place, measure where the wall studs are and write them down. Then take your pantry cabinet and slide it into place. Use your spirit level to check that the cabinet is level with the floor and wall. Another quick way to check this is to make sure all the feet are touching the floor. You can adjust the height of the feet manually.
Mark out where the wall studs are in the back of your cabinet, using the measurements you took in STEP 2. Remember to add the 20mm thickness of the end panel to your measurements. Then take your drill and simply screw the cabinets onto the wall studs.