Pronouns
Let's talk about Pronouns!
When you want to use le and lo next to each other, le becomes se. It's the same with other combinations of le/les and lo/la/los/las.
Ana le compra chaquetas. Ana se las compra.
Juan les compra un carro. Juan se lo compra.
When there are two verbs in a sentence, like in estoy comprando, you can put words like se and lo before the first verb or after the second one, but not in between!
Yo se lo estoy comprando.
Notice the different placement of words like te, me, lo and so on in the two types of commands!
Señor, cómpremelas, por favor.
Señor, no me las compre, por favor.