We've seen how to use le or la to say things like Elle le voit and Elle la voit.
To say to him, to her, or to it, you'll use lui instead. Keep in mind that some French verbs use à when we wouldn't use to in English!
Notice that the à disappears as well when you use lui.
To say to them, you'll use leur.
And remember, the words lui and leur come before the verb, not after!