Short answers, pulled from the story.
The four 1949 Geneva Conventions cover, respectively, wounded and sick soldiers in the field, wounded, sick, and shipwrecked members of armed forces at sea, prisoners of war, and civilian persons in time of war. They were adopted in response to the inhumanities of World War II and have been ratified by 196 countries.
Henry Dunant, a Swiss businessman, inspired the creation of the Geneva Conventions after visiting wounded soldiers following the Battle of Solferino in 1859. His 1862 book A Memory of Solferino led to the founding of the International Committee of the Red Cross and the first Geneva Convention in 1864. Dunant became co-recipient of the first Nobel Peace Prize in 1901.
The four 1949 Geneva Conventions have been ratified, in their entirety or with reservations, by 196 countries. They are among the most widely ratified international agreements in existence, alongside the UN Charter.
A grave breach of the Geneva Conventions is the treaty's legal definition of a war crime. Grave breaches include willful killing, torture, inhumane treatment, biological experiments, compelling protected persons to serve in an enemy's armed forces, unlawful deportation, hostage-taking, and wanton destruction of property not justified by military necessity.
Common Article 2 applies to international armed conflicts between states, while Common Article 3 applies to non-international armed conflicts where at least one party is not a state. Common Article 3 sets minimum protections including prohibitions on torture, hostage-taking, and executions without a fair trial, but does not govern methods and means of hostilities the way the full conventions do.
Three Additional Protocols supplement the 1949 Geneva Conventions. Protocol I (1977) covers victims of international armed conflicts, Protocol II (1977) covers victims of non-international armed conflicts, and Protocol III (2005) established the Red Crystal as an additional protective emblem for medical services alongside the Red Cross and Red Crescent symbols.