Since you are playing the Queen Gambit, 2.c4 is indeed the most logical way to continue. The main answers, 2...d5 and 2...Nf6, should fit in your repertoire anyway. The alternative is to go for 2.Nf3 first.
Move order finesses
Black's move order bears three subtelties:
You are offered a choice to switch to a French opening with 2.e4. This is probably your opponent's secret hope and since you are a 1.d4 player, you will probably not want to go down that road even though 2.e4 is of course a good move - unless you are fond of playing against the French defense.
After 2.c4, Black can bring the game to original territory with 2...Bb4+. This is a decent line, but not overly dangerous, and you can handle it with general rules (develop, avoid doubled pawns, castle...) if reaching an equal position suits you. Or you can learn a bit of theory about it, although at 700-900 level there are a lot of more important stuff for you to study.
If you want to avoid it altogether, you can start with 2.Nf3. Then 2...d5 3.c4 is back to QGD, with an early Nf3, which might or might not suit you depending on your favorite line of Queen Gambit. Note that 3...Bb4+ remains a decent option for Black.
Dutch players often start with 1...e6 to provoque 2.c4 and reduce their opponent choice: after 1.d4 f5 White often goes 2.g3 or 2.Nf3 and plays c4 only a few moves later, or even plays subvariations like 2.Bg5 or 2.e4, but after 1.d4 e6 2.c4 f5 those options are lost. If you play an early 2.c4 against the Dutch anyway, you won't mind those shenanigans at all, otherwise 2.Nf3 might once again be the solution.
Finally, some Black players also intend 2...b6 or other rare moves you should not be too worried about.
1...e6 is a decent move that plans to reach normal positions while limiting your choice. Those move-order subtelties are interesting when building your repertoire, yet they should not worry you too much until you reach a level around 1800 or so.
The natural alternative for a Queen's Gambit player is between 2.c4 and 2.Nf3; both have pluses and minuses. If it fits your usual way of playing in the QGD, go for 2.Nf3 first before 3.c4 and go for standard, QGD-like development: that avoids 2...Bb4+ tricks and requires less specific work on opening lines that shouldn't be your biggest concern right now.