First and Second Endings are used when part of the previous music is repeated but has a different ending. At the finish of the first ending (the measures under the bracket with a 1) there is a repeat sign at which you will return to either the beginning of the piece or to a repeat sign that faces the other direction . The music is then played again, skipping the first ending and playing the second ending instead.

Page 1, notes on the 5th string

Notes on the 6th String