can someone tell me how does this circuit works? and how to limit it to 1A using this circuit

there is some details in the link but i dun understand

http://www.electro-tech-online.com/articles/adjustable-low-drop-current-limiter.660/

thanks guys, much appreciated

 

Increase R1 to 1 Ohm. Adjust the pot U1 to set the 1A limit.
When the voltage tapped off at the pot wiper produces >0.6V between Q1 base and emitter, Q1 turns on and pulls the gate of M1 high, tending to turn it off.

 

Note that as the P-MOSFET gate-source voltage difference is reduced (Vgate becomes higher) it starts to turn off.