Buttons can be grouped in four possible ways:
•Use the Group tool:
First way:
Select close tools and put them into a group with the context menu.
Second way:
Press button: 
(on the additional panel of the context menu). Then you can drag necessary buttons into the group and add separators.
•Unite Buttons into common boundaries:
Use buttons on the additional panel of context menu of the button: 
select individual or neighboring buttons, e.g.:
•Use separtors.
•Unite buttons into dropdown lists or panels.