There are four symbols in common usage which indicate that a portion of music be repeated.
Two dots placed before a double bar line indicate that the music is to be repeated, from the beginning of the piece of music or from a previous set of repeat signs.
A diagonal line with a dot either side, indicates that the previous bar only is to be repeated.
The number 2 placed over a bar line crossed with two dotted diagonal lines, indicates that the previous two bars are to be repeated.
Diagonal lines are used to indicate that a ¼ note length (1 beat) of information per diagonal line, be repeated from the same position of the previous bar. These are used so that fills or variations of less than 4 * ¼ notes in length can be easily added to repeated rhythms e.g.: