What is the Geneva Convention?
It is a treaty, signed by all civilised nations, that prescribes the rules for conducting war. It specifies how prisoners are to be treated, it specifies how civilians in occupied territories are to be treated. It makes it illegal to do certain things like shoot at hospitals or houses of worship unless the enemy are shooting from them or storing weapons and ammo in them. Michael Montagne
Note that there is no "Geneva Convention". In reality, there are a series of international treaties, collectively called the "Geneva Conventions" (note the plural).
Collectively, these treaties (plus a set of similar treaties known as The Hague Conventions) set out a framework of rules regarding the "proper" or "civilized" conduct of warfare. They ban the use of certain weapons, and talk about how soldiers and civilians are to be treated during warfare. They also talk about proper conduct of warfare, addressing such topics as proper use of force, permitted actions by belligerent and non-belligerent forces, and identification of belligerents.