To play the E note, pick the open 1st string.
Play the F note with the first finger of your left hand just behind the first fret of the 1st string.
Play the G note with the third finger of your left hand just behind the third fret of the 1st string.
As a general rule:
Play notes on the first fret with your first finger.
Play notes on the second fret with your second finger.
Play notes on the third fret with your third finger.
The following example makes use of the notes E, F and G on the first string. As you move from F (1st fret) to G (3rd fret) leave your first finger on the F note. This will create a smoother sound when you return from G to F. Remember to play on the tips of your fingers and use all downstrokes with the pick. Listen carefully as you play and make sure your notes are clear and even. To help you develop a good sense of time, always use a metronome and tap your foot on each beat. There are two ways to practice this exercise: one is to name the notes out loud as you play and the other is to count as you play. Use both these methods until the exercise becomes easy.