Battery Power Control with MOSFET - One Button FlipFlop
Initially, C1 is discharged.
When the button is pressed, the gate of Q1 is pulled low trough C1, turning Q1 on.
This, in turn, turns Q2 on because it's gate is pulled high by Q1.
Q2 keeps Q1 on by pulling Q1's gate low trough R4.
So the 2 FET's keep each other enabled, the circuit is turned on.
When you let go of the button, C1 will charge up trough R1.
So next time you press the button, it will pull Q1's gate high, turning it off.
With Q1 disabled, Q2's gate will now be pulled low by R2, turning it off as well.
C1 can now discharge trough R1 and R2, so next time it's empty again and the cycle can repeat.