Taking an objective the enemy team was killing, by landing the last hit, usually with Smite. Baron and dragon are the classic targets.
team chat
in full english
I have no Smite, but I can try to steal it.
the context
"go steal" or "try steal" is typed when the objective is low and you do not control the pit: a gamble, one hit at the right moment. "stole" or "stolen" states the result. Not to be confused with "ks", which is about a kill.