As a chess player it is necessary that you learn this popular chess opening.
Learn the Queens Gambit Declined / Exchange Variation as this is an important chess opening, where vital chess strategies can be studied. Especially when you are a d4-player you must know this opening well.
This is a closed opening system where the positional knowledge and feeling and the positional abilities of a player are more important than theoretical and tactical considerations which arise after playing 1.e4 as first move. In this case more forced lines arise which makes it necessary to learn a lot of theorie and memorize a lot more chess variations. This is the reason why players like Korchnoi like to play 1.d4 ( or 1.c4) most of the time.
My friend, if you have a bad memory and don't like to learn a lot of forced theoretical variations then you should become a d4 player and study something like this opening here. Just grasp the positional ideas and apply them in your next game.
In the group of top Grandmasters with a rating of 2600 Elo and higher more than 70% of them are playing as first move 1.d4! Even Kasparov plays 90% of his games 1.d4. Please consider this.
You can castle long or short. This depends on the position of course. You must evaluate the time factor. Is Black able to attack your king faster or will you be able to attack the black king faster when you castle long?
The safe center makes it possible to attack with pawns on queenside or kingside. If you castle long you let run your pawns on the kingside, if you castle short you might let them run on the queenside and play the Minority Attack.
Garry Kasparov (chess champion) about Queen's Gambit Declined - Exchange Variation
Garry Kasparov (former world chess champion) about Queen's Gambit Declined - Exchange Variation