I mostly type circuits as "ccts".
Well - you can see the confusion it caused me; I figured it was an acronym of some sort, as the rest of your sentence was formed properly - had the rest of your sentence looked like textspeak, I probably would've interpreted it differently in the context.
I am trying to install a 24v 300w motor into a push scooter. I want to input a speed control, basically just increasing or decreasing the speed, through a potentiometer i guess. I a not able to decide the circuits that I should be considering in order to achieve this.
Well - it sounds like you want a simple PWM drive system; I would start with a 555 astable-multivibrator, whose frequency output (square wave) is controlled by a potentiometer:
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That's one example - tons abound on the 'net...
The max current from the motor is 9A. So the speed control circuit should be able to handle current upto 9A.
I'd design for more than that; maybe 50 percent more - so figure about 15 amps. Still, that should be fairly simple. If your motor only has to turn one way, drive the 555 circuit above with 12 volts (VCC), and the output should be around 10.5 volts, strong enough to feed into a standard high-current capable N-channel MOSFET, to drive the motor (you may need/want a heatsink on the FET):
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I can't vet that top circuit, but it appears similar to what you want (although you may or may not need the resistors prior to the gate input on the FET; I'm not sure what the 555 can handle current-wise, you may need to drive a transistor with the 555 to act as a buffer to drive the FET).
Hope this helps, or at least gives an idea of what to do...