Opening Raise Amounts NL Holdem

[Robbr25]

I have heard general advise about "standard" raises preflop.
For a standard NL table,
usually people say 3X the BB.
Does that mean you raise it 3X the BB or to 3X the BB?
e.g. $25/$50 Blinds do you raise it to $200 or $150?
Also, I see some that raise it to 3X the BB + a small amount (like $15 at $25/$50 blinds). Why the extra little amount?

As a side note, what about Heads up on the button?
Many say you should raise every time. How much should the raise be?
Any comments about Heads up NOT on the button? How much do you raise there? Does it depend on whether the button limps in? or raises?