First remove the crank bolt.
Now, if you have splined cranks some pullers require you to place a screw in the bolt thread in order to push out. Others require that you change the tip on the inner piece for splined vs. square taper.
Now examine your crank pulling tool. There is an outer piece with wrench flats and an inner piece that threads into the outer piece.
Back the inner piece out as far as it will go. You can remove it entirely, it will be fine.
Put a little grease on the outer piece threads to make sure things go in smoothly. Than thread it into the crank extraction threads that are on the inside of the crank spindle. It should go in smoothly, if you feel it isn't, stop and start again. Those are fine threads and disturbingly easy to cross-thread (which will ultimately ruin your cranks). Once that piece is in the threads, go ahead and use a wrench and tighten it down as well as you can. It does not remove the crank but the farther you sink it the less likely you are to rip the threads out.
Now thread the inner piece into the outer piece and just tighten down. The crank will come right out.