LOL. It's used to hydraulically remove bushings or bearings from small blind holes. Such as in a starter or plow motor end cap, cam bearing, bushed shafts in gear mechanisms, needle bearings from ends of gear shafts, etc. Removing the bushing from a flywheel would be a larger example it could be used on if you were shy the proper blind hole puller.
Punch needs to fit closely the bore of the part being removed. Pack the hole with oil soaked wadding and tap the punch in. Pressure from behind drives the bushing or needle bearing cage out. Add more wadding as the part pushes out.