Above measure 3 there is a symbol that looks an S with a diagonal line & 2 dots.  That's called a 'segno', literally 'sign' in Italian.  That's the musical direction indication that you should be ready at some point to return to this measure.

Then later at the end of measure 12 there is the matching musical direction indication 'del segno', literally 'from the sign' in Italian.  That's the indication to go back to the measure with the segno sign.

See attached image.

Hope that helps!