What you need when put on nail polish?

I don't know that I need to put on the based coat nail polish then the nail polish after that the top coat nail polish. I learn from my friend, she told me about it. I know of this last year, I have bad habits I have pink nail clipper but I don't use often as I would peel my nail. Peeling the nails make my finger hurt and sometimes bleed now I try as often as I can to use the nail clipper. I put on nail polish can avoid me from bite the nails or peel the nails. I don't have long nails, I try to keep them long before it is nice but then now I am keeping them shorts and clean.