Customary International Humanitarian Law: Laws of Warfare

The OP is from the International Committee of the Red Cross, which is the/a authoritative source. Also, compliments to their design, which makes a complex, somewhat intimidating topic quite approachable.

For some expert analysis for the current issue, the war in Gaza, see this post in a blog by leading experts:

https://www.justsecurity.org/89489/expert-guidance-law-of-ar...