H Bridge

MOSFET as a switch
https://www.electronics-tutorials.ws/transistor/tran_7.html

555 Timer
https://www.electronics-tutorials.ws/waveforms/555_timer.html
https://howtomechatronics.com/how-it-works/electronics/555-timer-ic-working-principle-block-diagram-circuit-schematics/

PWM
https://www.arduino.cc/en/tutorial/PWM
https://www.electronics-tutorials.ws/blog/pulse-width-modulation.html

H-bridge
https://hackaday.com/2014/04/25/a-h-bridge-motor-controller-tutorial-makes-it-simple-to-understand/