smart cast = doing something without clicking (say shooting spell in your cursor's direction by just pressing q)
s key = stop attack. makes your character not autoattack nearby minions/champs. useful for hiding in brushes, not pushing the lane, canceling autoattack animation, etc.
attack move = makes your character autoattack the nearest nearby thing (so minions, jungle monsters, champions, wards, tibbers, everything) by just clicking anywhere on the screen. pretty useful to kite if you're bad at adc like me
also my setup is:
qwer for spells
shift qwer for spells smartcast
ctrl qwer for spells level up
ctrl 1234 for lux laugh
all items set to smartcast with and without shift (so i don't accidentally miss dfg somehow), 4 for trinket, my extra mouse button for dfg (would be slot 4) and t for slot 6
s for stop
shift a or shift right click for attack move
x for shop (i just spam s for the old x thingie)
smartcast indicators on