I'll give a quick primer.
Shot size: bigger number means smaller shot.
-Size 9 is useless
-Size 8 is OK clays in close, or dove/quail
-Size 7 1/2 better for clays, dove, quail (IMHO)
-Size 6 good for partridge
-Size 4/5/6 good for pheasant
Steel shot for ducks is a whole different story. SIze 2-1 for relatively close (over decoys). Size 1-BB for farther out. BB to T for geese?
Buck for animals. Same thing. Smaller number=bigger shot. 000 is bigger than 00.
Oz of shot? More shot=denser patterns. Also more recoil. Also less velocity for a given number of drams/equiv.
Drams equiv? More drams= more powder=more velocity=more power and more recoil.
Max Drams and 1 1/8 oz shot is going to recoil a lot more than 7/8 oz shot and 2 3/4 drams. But will give fuller patterns and hit harder. Use the latter load for practice/skeet. Bigger loads for hunting or sporting clays.