Sideflips are certainly one of the easiest, but not necessarily where you should start. A backflip will be the easiest to learn, but front flips will probably be easier for you to get yourself to do. If you can find a gym with a trampoline or foam pit, that will help tremendously. If you can find a trampoline, start looking up tutorials for a backflip and prepare yourself to do one, then find someone who knows how to spot, and have them spot you for the back tuck. Once you have it solid on the trampoline without bouncing, take it to a tumble track, and then the floor. This process will work with most flips. Front flips you can usually just throw right away, then modify the technique, just remeber to go up and tuck.