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.
Here is an example using the notes E, F and G on the first string, along with B, C and D on the second string.