How do you use direct object pronouns in French?

To avoid repeating ourselves in English we often replace a noun with it.

In French we use the direct object pronouns: le, la and les in place of their respective gender noun. They come before the verb, and are abbreviated to l' if they are directly before a vowel or silent h. For example:

Tu vois le dauphin dans la mer? - Oui je vois le dauphin dans la mer. 

We can shorten this with the direct object pronoun le.  Tu vois le dauphin dans la mer? - Oui je le vois.