To play the D note, pick the open 4th string.
Play the E note with the second finger of your left hand behind the second fret of the 4th string.
Play the F note with the third finger of your left hand behind the third fret of the 4th string.
Here is an example featuring the notes D, E and F on the 4th string. Take it slowly at first and count along with the metronome as you play. Remember to use alternate picking for all the eighth notes.