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.
You now know two G notes. The open 3rd string and the third fret of the 1st string. These two G notes are said to be an octave apart. As a general rule: