Take a look at the two sentences. They are similar; yet, they have different meanings. What is the difference?
'Throw it to him.'
'Throw it at him.'
As you can see the prepositions in each sentence are different. Here's how the prepositions change the meaning:
This sentence means 'give it to him'. You throw it so that 'he' can catch it.
In this sentence we are trying to hit 'him' - we are not interested in him catching it.
Let's use the same forms in another couple of examples:
'Throw my cell phone to me - don't worry I won't drop it!'
'Throw that pen at Simon - I'll give you a dollar if you hit him!'