You now have two G notes; the one above and the one at the third fret on the first string. This type of repetition occurs with all notes, since the musical alphabet goes from A to G, and then back to A again. The distance between the two G notes is called an octave (see Note Summary below).
The following exercise is in % time. % time indicates two quarter note beats per bar (it is rhythmically similar to * time).
It also introduces the tie, which is not played, but its time value is added to that of the note before it.