This Army Training film explains the principles of operation of the M1 (Garand) Infantry Rifle

The US Rifle M1 was the first semiautomatic rifle to be the standard small arm of the US Military, requiring a trigger pull to fire a round but automatically chambering the next round.
This not only greatly increased the rate of fire over boltaction rifles, but made it far easier to reacquire a target after each round.
It was also the first semiautomatic rifle to be adopted by a major military power.
It was the product of a genuine genius, John Cantius Garand.