You will need a tool to pump air in to the combustion chamber to keep the valves closed. I use the hose from my compression tester after removing the schrader valve from the spark plug end. I plug in the other end ( gauge end )in to shop air. The spring compressor in the pic is for stud mounted rockers. There is a similar tool for shaft mounted rockers. You can do one cylinder at a time ( intake and exhaust ) by setting that cylinder at TDC on the compression stroke. Once you have the cylinder you are working on at TDC and aired up, you will want to smack the valve spring retainers with a soft mallet ( rubber / plastic ) to loosen the keepers before you compress the springs.