For example, there are many, many problems with the queen's gambit declined variation that you listed, but one of them is that neither player has taken the time to develop his pieces. It will help you understand basic variations of many openings and teach you basic ideas like, for example, don't move too many pawns in the opening, or don't move a piece (or a pawn) twice, or develop your pieces quickly and effectively.
You should buy this book, Improve Your Opening Play, by Chris Ward ( ). Eventually, as you get better at chess and understand these openings better through practice, you will understand why the two variations you listed are bad (and hence not the main lines of the opening). You can play d5 as black and play the queen's gambit accepted or declined.
If you are a beginning player, play e4 as white.
