Welcome to the board. This question has been asked in various ways - many times. If you look at the very top of the page, you will find "search". Go there & type in castration - you should get more than enough answers to confuse you.
This is a very debated subject. Many have strong opinions, like myself. We castrate with a scapel & cut the testicles out. We do it at birth if we KNOW we want him a steer, we cut again at spring work up in April, and again prior to fall weaning.
If you decide to use banding method, be sure to give them a shot for tetanus.