queens gambit response
White only gets one move at a time. White can't play the Queens Gambit unless black plays 1..d5 after 1. d4.
Then the Queens Gambit is offered with 2. c4. It is a gambit because the c4 pawn is undefended.
Black can answer 2.. e6 or 2..c6 or 2..dxc4.
There isn't a best one paragraph response. Read one of the many books to better understand the many responses.
1.d4 d5 2.c4
This is an opening that has one of the highest number of good options. Probably a dozen or more. There is no "best."
Look at GM games for a middlegame that appeals to you, then choose the opening that leads to it.
Possibly helpful: First Steps Queen's Gambit
https://www.newinchess.com/media/wysiwyg/product_pdf/7652.pdf