the flywheel puller looks like a nut with a bolt through it. you screw that onto the bolt in the middle of the flywheel (the metal magneto) and then screw the other part in the opposite direction. a set of fly wheel holders is also useful, but a monkey wrench can hold the flywheel from spinning just as well.
but w/o a flywheel puller you are not getting your magneto off. period.
if you're only dealing w/ changing the cylinder, all you need are socket sets (at least on puch and minarelli). minarelli uses 10mm sockets.
your bare essential tools should include:
screwdrivers (philips and flat)
metric socket set (including spark plug socket)
needlenose pliers (you'll need those to remove/replace pistons)
metric allen wrenches