To play the D note, pick the open 4th string.
Play the E note with the second finger of your left hand just behind the second fret of the 4th string.
Play the F note with the third finger of your left hand just behind the third fret of the 4th string.
This example uses notes on the 4th string along with the other notes you have learned. It contains two versions of D, E and F which are an octave apart. An octave is the distance between a note and its next repeat either higher or lower.
This is a sharp sign. A sharp sign written before a note on the staff means that you play the note that is one fret higher than the written note. The following diagram illustrates two F sharp (F#) notes. A sharp sign is always written before the note on the staff. A sharp sign applies to all following notes of the same pitch within that bar. The sharp sign is cancelled by a bar line.