Avant de rentrer, nous fermons le portail, nous posons l’arrosoir près des pots, et nous regardons une dernière fois la pelouse depuis la terrasse.

Because after avant when you mean before doing something, French normally uses de + infinitive.

• avant de rentrer = before going back in / before returning
• avant de manger = before eating
• avant de partir = before leaving

So de is required here.

It stays in the infinitive because it comes after avant de.

French often uses this pattern:

• avant de + infinitive
• après + infinitive past form in some cases
• sans + infinitive
• pour + infinitive

So rentrer is not conjugated because it is part of the structure avant de rentrer.

Rentrer usually means to go back in, to return, or to come home/back, depending on context.

In this sentence, it most likely means something like:

• before going back inside or
• before returning

Since the rest of the sentence describes actions done outside in a garden area, before going back inside is the most natural understanding.

French often uses the present tense to describe:

• habitual actions
• routines
• a sequence of actions
• vivid narration

So this can sound like:

• Before going back inside, we close the gate, put the watering can near the pots, and look one last time at the lawn from the terrace.

It may describe a regular routine or simply narrate events in a straightforward way.

Yes, French could leave it out after the first verb:

• Avant de rentrer, nous fermons le portail, posons l’arrosoir près des pots, et regardons...

That is grammatically possible.

But repeating nous:

• makes the sequence clearer
• gives the sentence a more deliberate, rhythmic feel
• emphasizes each action separately

So the repetition is natural, even if not strictly necessary.

Le portail usually means a gate, especially an outside gate, often for a garden, yard, or entrance to a property.

La porte usually means a door.

So in this garden/outdoor setting:

• le portail = the gate
• la porte = the door

Because arrosoir begins with a vowel sound, and French usually contracts le or la before a vowel:

• le arrosoir → l’arrosoir
• la école → l’école

This is called elision.

So:

• le + arrosoir becomes l’arrosoir

Un arrosoir means a watering can.

It is the container used to water plants by hand.

So:

• nous posons l’arrosoir près des pots = we put/place the watering can near the pots

Because de + les contracts to des.

So:

• près de les pots → près des pots

This is a standard French contraction.

Other common ones are:

• de + le → du
• à + le → au
• à + les → aux

No. Here des is not the plural article meaning some. It is the contraction of de + les after près de.

So:

• près des pots = near the pots

This is a very common thing for learners to notice, because des can mean different things depending on context.

Compare:

• J’achète des pots. = I’m buying some pots.
• Je suis près des pots. = I am near the pots.

Same form, different grammar.

Because French regarder directly takes an object. It does not need a preposition like at.

So:

• regarder la pelouse = to look at the lawn
• regarder le ciel = to look at the sky
• regarder quelqu’un = to look at someone

This is different from English, where look usually needs at.

Une dernière fois means one last time.

French often uses un/une in expressions where English also uses a or one:

• une fois = once / one time
• une dernière fois = one last time

So une is part of the natural expression.

Yes, depuis very often means since or for with time:

• depuis lundi = since Monday
• depuis deux heures = for two hours

But it can also mean from, especially when talking about a point of origin or viewpoint.

Here:

• depuis la terrasse = from the terrace

It tells you the place from which they are looking.

Sometimes de la terrasse might be understandable, but depuis la terrasse is better here because it clearly expresses the viewpoint:

• regarder la pelouse depuis la terrasse = look at the lawn from the terrace

Depuis makes the spatial relation more explicit.

Because Avant de rentrer is an introductory phrase placed before the main clause.

The comma helps separate:

• the time-setting phrase: Avant de rentrer
• the main actions: nous fermons..., nous posons..., et nous regardons...

This is similar to English punctuation in a sentence like:

• Before going back inside, we close the gate...

Yes, it is natural because it links the last item in a series of actions:

• nous fermons...
• nous posons...
• et nous regardons...

Just like English uses and before the final action, French uses et.

It gives a short sequence of actions in order:

1. Avant de rentrer = sets the time: before going back in
2. nous fermons le portail
3. nous posons l’arrosoir près des pots
4. et nous regardons une dernière fois la pelouse depuis la terrasse

So the sentence is describing a little routine or final moment before leaving the outdoor space.