To toggle a breakpoint, position a cursor to the line of code and press F9:
You can toggle a breakpoint with a left mouse click left of the line of code, and the red circle that denotes a breakpoint will show up and dissapear.
To delete all breakpoints, press CTRL+SHIFT+F9 or go to the Debug menu -> Delete All Breakpoints:
To disable all breakpoints without deleting them, go to the Debug menu -> Disable All Breakpoints:
To open the Breakpoints window that lists all the breakpoints set in the current Query Editor, allows you to manage them, press CTRL+ALT+B:
You can open the Breakpoints window from the Debug menu -> Windows -> Breakpoints:
To start or continue debugging, press ALT+F5 or go to the Debug menu -> Start Debugging: