I'm pretty rusty but ill give you the basics.
Observer: "Hey you[callsign], this is me[call sign]."
Battery: "this is me[call sign], send your traffic."
Observer:"this is me, reqesting fire mission"
You will have preferably a 12 digit coord at least. You will also have pre determined "known distance" grids already set up. Intersections are pretty solid for this. You need to indentify what kind of targets are present so the gun bunnies know which shells to lob. Different ammo for different targets.
Once the round is sent battery will call out "splash over", the observer on the ground will call out "splash out" when he sees the impact. This lets the battery know you have eyes on where the target hit. Then you start dropping or raising by a set amount of increments. Im trying not to be too detailed here obviously. Once the round hit where you want it the observer would call up for a "fire for effect". An entire Battery will unload on that command.