Ce week-end, nous allons à la plage et Marie emporte son maillot dans un grand sac.

Because week-end is a masculine singular noun in French, so the correct demonstrative adjective is ce.

• ce = this / that for masculine singular nouns
• cette = this / that for feminine singular nouns

So:

• ce week-end = this weekend

You will also often see week-end written with a hyphen, though spelling can vary in modern usage.

French often uses the present tense to talk about a planned or near future when there is a clear time expression.

Here, Ce week-end already tells you the action happens in the future, so nous allons à la plage can naturally mean:

• We’re going to the beach this weekend

This is very common in both French and English. French could also use the future tense:

• Ce week-end, nous irons à la plage.

That is also correct, but the present tense sounds very natural here.

The verb aller usually takes à before a destination:

• aller à
  • place = to go to a place

Since plage is a feminine singular noun, it uses la:

• la plage = the beach

So:

• à + la plage = à la plage

Compare:

• au parc = to the park (à + le = au)
• à la plage = to the beach
• aux magasins = to the shops (à + les = aux)

There is no contraction with la, so it stays à la.

Yes. In French, the simple present can cover both ideas, depending on context.

• nous allons à la plage can mean we go to the beach
• or we are going to the beach

The time phrase Ce week-end makes it sound like a planned future event, so in this sentence English would usually translate it as:

• This weekend, we’re going to the beach...

So the tense is grammatically present, but the meaning is future because of the context.

Both are correct, but on va is usually more common in everyday spoken French.

• nous allons à la plage = correct, standard, a bit more formal or written
• on va à la plage = very common in speech

So in conversation, many native speakers would say:

• Ce week-end, on va à la plage...

But using nous allons is absolutely normal and good French.

Emporte comes from emporter, which usually means to take away, to take along, or to carry off with you.

Here it suggests that Marie is taking her swimsuit with her.

That is slightly different from:

• porter = to carry / to wear
• apporter = to bring
• emporter = to take away / take along

So:

• Marie emporte son maillot = Marie is taking her swimsuit along

In this sentence, it gives the idea that she is bringing it with her in the bag.

In French, possessive adjectives agree with the thing possessed, not with the owner.

The noun maillot is masculine, so French uses:

• son maillot = her swimsuit

Even though Marie is female, the word maillot is masculine, so son is correct.

Compare:

• Marie emporte son maillot. = her swimsuit
• Marie emporte sa serviette. = her towel

Why the difference? Because:

• maillot is masculine
• serviette is feminine

Here, maillot means swimsuit, but it is often short for maillot de bain.

So in beach context:

• maillot = swimsuit
• maillot de bain = swimsuit / bathing suit

Be aware that maillot can mean other things in different contexts, such as a sports jersey or similar clothing item. The beach context tells you it means swimsuit here.

French adjectives can come before or after the noun, depending on the adjective.

Grand is one of the common adjectives that often comes before the noun:

• un grand sac = a big bag

Many common short adjectives of size, beauty, age, and goodness often go before the noun. Learners sometimes remember this with the label BAGS:

• Beauty
• Age
• Goodness
• Size

Since grand is a size adjective, un grand sac is the normal order.

Yes. Dans un grand sac tells you where the swimsuit is or how Marie is taking it.

So the idea is:

• Marie is taking her swimsuit
• and it is in a big bag

Dans usually means in or inside.

So this part means something like:

• in a big bag

In natural English, you might translate the whole idea as:

• Marie is taking her swimsuit in a big bag
• or more naturally, Marie is packing/taking her swimsuit in a big bag

Yes, a few useful ones:

• nous allons has a liaison: the s in nous is pronounced like z before allons
  • roughly: noo-zah-lon
• à la plage: plage sounds like plahzh
• grand has a nasal vowel, and the final d is usually silent
• sac ends with a pronounced k sound

So a rough pronunciation guide would be:

• Ce week-end, nous allons à la plage et Marie emporte son maillot dans un grand sac.
• roughly: suh wee-kend, noo-zah-lon ah lah plahzh ay mah-ree ahn-port son my-oh dan zhun gran sak

That is only an approximation, but the main thing to notice is the liaison in nous allons.