Can someone help me please? I need to remove a virus from my computer.?

Why does anti-virus softwares claim to be able to take out any virus? ...but when you get a virus inside your computer and scan it to remove and it does NOTHING! Yes, I updated it. Still did not remove. Tried malwarebytes and it still didn't work. I'm very angry about this virus removal software. So, i'm stuck with this virus... and I want to learn how to do it myself. I don't want to pay $120 like I did last time. Thanx.