À côté du chiot, un chaton gris commence à miauler dès que la porte s’ouvre.

À côté de means next to or beside. It usually suggests a fairly exact position.

So À côté du chiot means the kitten is right beside the puppy.

Près de also means near or close to, but it can be a little less exact. In many situations the two are close in meaning, but à côté de feels more specifically like right next to.

Because de + le contracts to du in French.

The expression is à côté de + noun, so with le chiot you get:

à côté de le chiot → à côté du chiot

This is a standard contraction:

• de + le → du
• de + les → des

But there is no contraction with:

• de la
• de l’

So you would also get:

• à côté de la porte
• à côté de l’animal
• à côté des enfants

French often puts a place expression at the start of a sentence to set the scene.

So À côté du chiot, ... works like:

• Next to the puppy, ...
• Beside the puppy, ...

It gives the location first, then tells you what happens.

A more neutral order would be:

Un chaton gris commence à miauler à côté du chiot dès que la porte s’ouvre.

That is also grammatical, but the original sentence sounds more like it is painting a little scene.

The comma separates the opening location phrase from the main clause.

It is not always absolutely required with short introductory phrases, but it is very common and helps readability. Here it marks À côté du chiot as scene-setting information before the main action:

un chaton gris commence à miauler...

So the comma is more about style and clarity than a special grammar rule unique to this sentence.

They are the words for young animals:

• chiot = puppy
• chaton = kitten

So the sentence contrasts a young dog and a young cat.

Both are masculine nouns:

• un chiot
• un chaton

In French, most color adjectives come after the noun.

So:

• un chaton gris = a gray kitten
• une porte grise = a gray door

That is why you get chaton gris, not usually gris chaton.

Also, adjectives must agree in gender and number when needed:

• masculine singular: gris
• feminine singular: grise
• masculine plural: gris
• feminine plural: grises

Commence à miauler means begins to meow or starts meowing. It focuses on the start of the action.

If you said miaule, that would simply mean meows or is meowing, without emphasizing the beginning.

So the difference is:

• Le chaton miaule = The kitten meows / is meowing
• Le chaton commence à miauler = The kitten starts to meow

After commencer, French normally uses à before an infinitive:

• commencer à parler
• commencer à courir
• commencer à miauler

Miauler is the verb used for the sound a cat makes: to meow.

It is especially used for cats and kittens. So in this sentence it fits chaton perfectly.

French often has specific animal-sound verbs, for example:

• aboyer = to bark
• miauler = to meow
• rugir = to roar

Dès que means as soon as. It emphasizes immediacy.

So: dès que la porte s’ouvre = as soon as the door opens

That is a bit stronger and more precise than quand, which usually just means when.

Compare:

• dès que la porte s’ouvre = immediately when the door opens
• quand la porte s’ouvre = when the door opens

Both can work, but dès que highlights the direct trigger: the meowing starts right away.

In French, s’ouvrir is the usual way to say to open when the thing itself is the subject:

• La porte s’ouvre = The door opens

This does not literally mean the door opens itself in a logical sense. It is just the normal French structure.

Compare:

• Quelqu’un ouvre la porte = Someone opens the door
• La porte s’ouvre = The door opens

So ouvrir is used when an agent opens something, while s’ouvrir is often used when the object becomes open and no opener is named.

It is called elision.

The full form is se ouvre, but French does not keep se before a vowel sound. It shortens it to s’:

• se ouvre → s’ouvre

The same thing happens in many common forms:

• je aime → j’aime
• le ami → l’ami
• ne est → n’est

So s’ouvre is simply the normal shortened form of se ouvre.

French often uses the definite article when the thing is identifiable from the situation or context.

So la porte can mean:

• the door we already know about
• the relevant door in the scene
• the obvious door in that place

English sometimes uses the less often than French, so this is a common thing learners notice. Here la porte sounds natural because the sentence presents a specific scene, and the door is understood as part of it.

Yes. Both are in the present indicative:

• commence = present of commencer
• s’ouvre = present of s’ouvrir

French present tense can be used in several ways, including:

• a general or habitual action
• a scene being described right now
• a vivid narrative style

In this sentence, it could describe a regular pattern or a vivid scene:

• every time the door opens, the gray kitten starts meowing
• or a scene unfolding in front of you

French present is often a bit broader than English simple present.