This is intended for members of our choir who are not familiar with some of the indications in the written music that we use.
Written music has a few symbols to indicate that sections of the music should be repeated. The start of the section is marked by a thicker bar line with 2 dots to the right. The end of the repeated section has a thicker bar line with 2 dots to the left.
So, this section of music means that the 3 bars between the left repeat-sign and the right repeat-sign should by played or sung twice.
If I use the letters A, B and C as the names of these bars instead of showing the notes in them,
then the section above (with repeats) is a shorter way of writing it than as below (without repeats).
Obviously, if the repeated section has 20 bars instead of just 3, this can save a lot of writing.
Sometimes only part of a section is repeated. The unrepeated part of the section that is played only on the 1st pass through, is marked like this. The 1 might be written out in full as 1st time, or 1st time only.
On the 2nd pass through, you should jump past the 1st time section, and continue at the section marked like this.
So, this section of music
is a short way of writing bars ABC, then DE, then ABC again and then bars FG.