How did they form irrigation in ancient Egypt?

Most Nile irrigation takes the form of "flood irrigation", this is still commonly used today and occurs when the river rises (annually) in flood.

In ancient times they also used a counterbalanced device called a "shadouf" to raise water to irrigation trenches when the level of the river had dropped - again these are still in use in some rural areas along the Nile.

A more common method employed today uses concrete irrigation canals with water lifting pumps; these pumps raise the water from the river surface and into the canal where it is then distributed by smaller canals.

The height difference in the rivers surface (between the seasons) can vary as much as 12 to 18 meters.

The Shadouf is a device used to raise water from one level to another and onto the fields. Operated by hand, this device has a pole one end of the pole is a bucket. on the other end is a counter weight. The peasant farmer or slave filled the bucket with water, then let go of the bucket. The weight on the other end would raise the bucket of water allowing the contents to be tipped onto the field. This process went on all day long, day after day during the growing seasonhi.
The ancient Egyptian used a shaduf to get get water from the Nile to other farms for irrigation. The shaduf consisted of a long pole that was balanced on a wooden crossbeam. A counterweight was attached at one end and a leather bucket was fastened to the other end. The farmer would pull the rope and bucket down into the water. Once the leather bucket was full of water, he would let go of the rope and the counterweight would lift the bucket out of the water. The farmer would then tip the water out of the bucket into a nearby canal which would allow the water to travel to other farms.
when the Nile river flooded its banks and covered the land.As the river water gradually drained away they left behind a layer of silt