The dialog allows you to specify maximum of measures per line/system before you automatically layout the whole score. To open this dialog, click the menu Score->Layout... or button Layout from the Edit toolbar tab.

Note: For more information related to automatically formatting the score, please refer to the Auto Format help page.

Maximum Measures per Line:

This value controls maximum of measures every system. If the system space is not enough for maximum of measures, try to place less measures.