The ruler displays either the time, counting from the beginning of a musical piece, or the bar number.
Ruler context menu
Show Time - Switches the Ruler to Time mode. This is also the default mode of the Ruler.
Show Bars - Switches the Ruler to Bar Number mode.
Insert Bar - Adds a bar-line.
Remove Bar - Removes a bar-line.
You may also use the Tapping Tool to place bars.