Catapults are thought to have been invented by the ancient Greeks around 300-400 BCE. Early designs were basic arrow-firing mechanisms, similar to hand-held crossbows. As they developed they became larger and more complicated with winched pull-back systems and torsion springs.
The main use of catapults was on the battlefield. Alexander the Great was among the first Greeks recorded as having used catapults in battle. As the use of catapults became increasingly common, even Greek children were taught how to use them.
The Romans also used catapults in war. Their early machines were very similar to large crossbows.
In the medieval period catapults were used as 'siege weapons'. These catapults were large. Many were on wheels so they could be moved around and positioned to hit a target. They were used to breach the walls of castles and cities.
There were various designs of catapult during the medieval period, including the mangonel. The mangonel was used to throw heavy objects - or sometimes unpleasant items such as animal dung - from a cup-shaped holder on the end of its arm. (The model we are making in our session is similar in design to a mangonel.)
The trebuchet is also another well-known medieval weapon using a catapult design.
Reconstruction of a medieval trebuchet at Warwick Castle, England:
Catapults have been used in war right up until the early 20th century. At the beginning of World War I soldiers used catapults to fire hand grenades from the trenches.
Nowadays catapults are less likely to be used in war and more likely to be used in recreational activities.
For an introduction to the physics of catapults real world physics problems is quite a good site.