Different types of bar lines communicate specific instructions to the performer:
: A double bar line accompanied by two dots. If the dots face left, the performer must repeat the previous section; if they face right, they mark the start of the section to be repeated. bar line
: Two thin vertical lines that indicate a significant change in the music, such as the end of a section, a key change, or a shift in tempo. if they face right
: The most standard vertical line, used to mark the end of one measure and the beginning of the next. a key change