If you set a breakpoint to a certain line and select Start Debugging (F5), it'll stop at the breakpoint and from there, you can do things with a debugger. I can't tell you specifically what you'll be able to do with a debugger since I did not master assembly and RCE/RE completely.
If you set a breakpoint and start without debugging (CTRL+F5), it will ignore the breakpoint and execute the program.
That's just the basic.