What is first copy or Copy B of Form(s) W-2?

I need to file my returns my mail and it was written that I need to attach the first copy or Copy B of Form(s) W-2 to the front of your Form 1040.

What is first copy of W2?
Copy B of Form W2 means the left corner sheer that can be teared off from original W2?

Is it ok to print the electronic copy of W2 when filing by mail?