Looping code in a form?

I have been trying to figure out how all this works, but I think I may be trying to do this the wrong way. Anyway, I am trying to make a simple program pressed a key after every 10 second but you can change the time between keystrokes by typing in the delay time in a form. I have a button which turns this on and off.

I do not understand how to make a code which just presses the key every 10 seconds (or however many seconds inputted).

I have got as far as pressing a button to change a text box value, and I have managed to make it press the key after the inputted seconds, but I don't know how to make it loop until I press the button again.

Many thanks for any information