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.
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.
See Voltas, for repeat sections with multiple endings.
To change the number of times the repeat section is played, adjust the Play count of the final measure in the Measure properties dialog.
Ignore Repeat barlines, Jumps, Markers playback by unchecking Play toolbar : Cogwheel → Play repeats, see Playback controls chapter.
Do any of these as required
See the main chapter Templates and styles
Values of the "Style for Barlines" can be edited in Format→Style→Barlines. Specify thickness, distance etc.