MuseScore -- Index -- Volta

Volta brackets are used to mark different endings in a repeat:

Sample first and second endings

Volta brackets can be place on the score by drag-and-droping from the lines palette.

The brackets can span more than one measure. Double click the volta to enter edit mode and then move the handles with:

Shift + Right   one measure left
Shift + Left   one measure right

This commands move the "logical" start or end of the volta which determine the bracketed measures. Other commands in edit mode also move the handles but do not change how the repeat is played. If you move the handles, a dashed line from the logical position to the actual position is shown

Second-ending volta in edit mode

Properties
Repeat List
This list determines which repeat the volta should be played. If the volta is played in more than one repeat all repeat numbers must be listed and separated by a comma (",").

Text
You can set an arbitrary volta text. Of course the text should correspond with the repeat list.
Volta Properties dialog

Sample first-through-fifth ending followed by sixth ending