Direct Objects receive the verb's action and answer "What? or "Whom?".
Example: Bill hit the ball. The WHAT? The BALL.
Te conozco. (I know you)
La come. (He/She eats it.)
If both DIRECT OBJECT and INDIRECT OBJECT pronouns are used, the IOP COMES FIRST. If "L" is the 1st letter for both the IOP and the DOP, then the IOP is changed to 'SE.'
Object pronouns usually are placed before the conjugated verb, but if it is a compound verb, it can be attached to the end of the 2nd verb (but it doesn't have to be).
Lo quiero vender / Quiero venderlo - I want to sell it.
Me voy a lavar / Voy a lavarme - I'm going to wash up.
When double pronouns are attached to an infinitive, an accent must be added to the last syllable of the infinitive, in order to maintain the correct stress on the word.
Quiere vendérnoslo - He wants to sell it to us.
Voy a dártelo - I'm going to give it to you.
Object Pronouns with Present Participle
When pronouns are used with a present participle or progressive tense, the pronoun(s) can either precede the helping verb or be attached to the participle.
Lo estoy mirando / Estoy mirándolo - I am watching it.
Las estábamos mirando / Estábamos mirándolas - We were looking for them.
Note that when the pronoun is attached to the 2nd verb, an accent must be added to the originally stressed syllable in order to maintain the correct stress on the word.
Object Pronouns with Imperative
When object pronouns are used with negative commands, they precede the verbs (You'll learn about these later). However, for affirmative commands they must be attached to the end of the verb.
¡No me ayudes! - ¡Ayúdame!
Don't help me! - Help me!
No se vaya (Ud.) - Váyase.
Don't go away. - Go away.
No lo comas - Cómelo.
Don't eat it - Eat it.
No me la traiga - Tráigamela.
Don't bring it to me - Bring it to me.
Again, when object pronouns are attached, an accent must be added to the verb to maintain the proper word stress.