The D minor seventh (Dm7) chord is a four-note chord formed from the notes, from lowest to highest: D, F, A and C. Minor seventh chords are minor triads with a minor seventh above the root added to the chord. The added minor seventh gives the chord a dark, jazzy sound.c 

Dm7 chords sound complicated but aren't much more difficult to play than a simple D minor triad. To play a Dm7 chord start by playing a D minor triad. Place your right thumb on D. Now, place your middle finger on F. Finally, place your little finger on A. In order to turn your Dm triad into a Dm7 chord, cross your left index finger over your right hand and place it on C. Play all four notes at the same time, keeping the volume consistent. 

With practice you can also play a Dm7 chord with one hand. To play a Dm7 chord with your right hand, place your right thumb on D, your index finger on F, your middle finger on A and your little finger on C. This might take some practice so try your best not to get frustrated. In time you'll get it down.