Welcome shurhad, good choice in using the HeadBlade. It takes a little time to get used to but once you do, it's great.
You should not use any pressure on the blade end. Keep the wheel end on your scalp with little pressure and let the fingers rest on the unit, this will keep the blade end in place. Take long strokes with the grain when you first begin. For the knots and pimples, I would let the pimples heal before shaving again. If you have any moles that are being cut, you may want to look into having them removed. Good luck with the shaving.