I am a licensed hairdresser. I would not attempt to razor cut my own hair.
i am not a big fan of using the razor on most people. If you have curly, course or frizzy hair, a razor cut will make it worse. It also splits your hair shaft.
Think of a strand of hair is a stalk of celery. Now imagine running a vegetable peeler down it. It will strip the top layer of the celery away. That is what a razor will do to your hair.
Razor cuts are okay if you wear you wear your hair short and get it cut often, but if you have medium length hair and decide to grow it out, you will have a whole lot of hair damage to cut away.
I am also not a fan of putting hair into a pony and cutting it. I have had to correct a lot of bad haircuts over the years. It is much better to section the hair and pull it up. let down a little at a time and cut a little. Bring down another layer to meet the cut hair and cut again.
Bangs are easy to cut. Start cutting in the middle (center of your nose for a guide) to the side. Then cut the other half starting from the other far side to the middle. Go slow and cut small portions. Remember to cut hair while wet and it will dry and shrink up a little.
Cutting hair is like painting on canvas. An artist can show you, you can do as you are taught, but unless you have talent, it won't turn out well.