'le' and 'la'

So hang on a minute, don't le and la mean the? What's the big deal?

Well, they generally do. There's actually a whole discussion that I'll save for another time on cases where le and la before a noun don't translate as the. (Consider, for example, the expression prendre l'apéritif, which it would be nonesensical to translate as to have the aperitif.)

But for now, I want to highlight the use of le and la as pronouns. When placed before a verb[1], they mean him, her, it. For example:

Tu connais mon oncle? Oui, je le connais.
Do you know my uncle? Yes, I know him.
Tu connais ma mère? Oui, je la connais.
Do you know my mum? Yes, I know her.
Tu vois ce bâtiment? Oui, je le vois.
Do/can you see that building? Yes, I (can) see it.
Tu vois la cathédrale? Oui, je la vois.
Do/can you see the cathedral? Yes, I (can) see it.

Before a vowel sound[2], le and la are always shortened to l'. In practice, this generally includes all of the perfect tense:

Je l'aime bien.
I like him/her.
Je l'ai vu hier.
I saw him/it yesterday.
Ta soeur? Non, je ne l'ai pas vue.
Your sister? No, I haven't seen her.

Notice that in writing, -e is added to the past participle when la or (feminine) l' comes before the verb-- in other words vu is written vue in this last example. This rarely affects the pronunciation, though.

Notice that in French, when referring to a specific thing or person, it's common to form so-called dislocated sentences, in which you use both le/la/l' and the noun phrase that it represents:

Je l'ai vu hier, ton frère.
I saw your brother yesterday.

See the grammar section on French object pronouns for some more information on these and related pronouns.

[1] There are some cases where these pronouns are attached to the end of the verb, which we don't deal with here.
[2] When followed by the so-called h aspiré, which technically is classed as "neither a consonant nor vowel", le and la remain, and the vowel of le must be pronounced: je le hais, not je l'hais.