A well is a hole that is dug into the Earth to get a fluid. Most wells are to get water. There are also oil well s and gas wells.
A qanat is an ancient complex water well system used in the Middle East. Wells can be as simple as a hole that a bucket on a rope can be lowered into, or very complex with pipes and high-powered pumps to get the water out. Most cities that are not close to fresh waterlakes or rivers get their water from wells.
It is important to be careful what rubbish is put into the ground near a well. If something toxic is put in the ground, it could go in the groundwater and the well and make people sick.