A repeat sign looks like a double barline with a dot above and below the center line of the staff (see image below). It is used to enclose repeated sections of the score.
Adding repeat signs to your score
Place a start repeat barline at the beginning of the repeated section and an end repeat barline at the end.
If the start of the repeat section coincides with the beginning of the piece there is no need for a start repeat barline.
Multiple ending repeats
See Voltas, for repeat sections with multiple endings.
Changing playback of repeat signs
Changing appearance of repeat signs
In the Properties panel, you can specify repeat barlines with winged tips in "Barlines: repeat style".
See Changing appearance of repeat signs (above).
You can specify repeat barlines with winged tips, and change the distance from the barline to dots for all repeat barlines in Format→Style→Barlines.