Let's take a look at the phrasal verb step on. Here it can be seen as having two meanings:
1) Step on - Usually 'step on it', is an informal way of telling someone to move quickly or to hurry up.
'Step on it, taxi driver, or i'm going to be late for my flight!'
'We'd better step on it, or else we won't arrive in time.'
2) Step on - Usually 'step on something', is used to mean 'stand on' or 'put your foot on top of something'.
'Careful! Don't step on the cat!'
'Look! A cockroach! Step on it!'
