Objeto directo e indirecto

Do you know what the direct object complement is?
Native speakers use direct object complements a lot to avoid repeating the same words over and over again. For example:
I saw some dogs in the park. I saw them in the morning when I was walking. 
He visto unos perros en el parque. Los he visto esta mañana cuando caminaba.

But there is also the indirect object complement, which is expresses the recipient or beneficiary of the action. Tip for identifying the indirect object: answer the question "to whom? For example:

Compré un regalo para mi hermana. Le compré un regalo.

I bought a present for my sister. I bought a present for her.