L’amortisseur est sous la voiture.

Because amortisseur begins with a vowel sound, French normally uses elision: the vowel in le drops before a vowel or silent h.

So:

• le amortisseur → l’amortisseur

This is very common in French:

• l’homme
• l’école
• l’amie

Here, l’ can stand for either le or la, but in this sentence it stands for le because amortisseur is masculine.

The article tells you: l’ here is short for le, so amortisseur is masculine singular.

You can also see this in dictionary entries, where nouns are often marked:

• un amortisseur = masculine
• une voiture = feminine

So in this sentence:

• l’amortisseur = the shock absorber
• la voiture = the car

A rough pronunciation is:

a-mor-ti-seur

More accurately in IPA: /a.mɔʁ.ti.sœʁ/

A few pronunciation notes:

• r in French is the French r, not the English one
• ti here sounds like tee
• the ending -eur sounds a bit like euhr, but with a French vowel that does not exist exactly in English

If you want a rough English-style approximation, ah-mor-tee-sur is closer than reading it like normal English spelling.

Because sous is the normal preposition meaning under.

• sous la voiture = under the car

Dessous is usually not used directly before a noun like that. It is more often an adverb or part of another expression.

Compare:

• sous la voiture = under the car
• dessous = underneath / below

You can also say:

• en dessous de la voiture = underneath the car

But sous la voiture is simpler and more natural in a basic sentence like this.

La voiture uses the definite article, so it means the car rather than a car.

French often uses the definite article when the thing is:

• specific
• already known from context
• being pointed out as a particular object

So:

• sous la voiture = under the car
• sous une voiture = under a car

Both are grammatically correct, but they do not mean exactly the same thing.

Yes, in this sentence the structure is very similar to English:

• L’amortisseur = subject
• est = is
• sous la voiture = prepositional phrase showing location

So the pattern is:

subject + verb + location

That is why it feels quite straightforward for an English speaker.

Est is the third-person singular form of être, which means to be.

So:

• je suis = I am
• tu es = you are
• il / elle est = he / she is

In this sentence, l’amortisseur is singular, so French uses est:

• L’amortisseur est... = The shock absorber is...

If the subject were plural, it would become sont:

• Les amortisseurs sont sous la voiture.

No. Sous does not contract with the article.

So you simply say:

• sous la voiture
• sous le siège
• sous les tables

This is different from prepositions like à and de, which do contract in some cases:

• à + le → au
• de + le → du

But:

• sous le stays sous le
• not soule or anything like that

It can suggest either, depending on context.

Most naturally, sous la voiture means under the car in terms of location. In real-life context, since a shock absorber is a car part, a listener may understand that it is part of the car’s underside or suspension area.

If you wanted to be more precise, French could use wording such as:

• fixé sous la voiture = attached under the car
• situé sous la voiture = located under the car

But your sentence is perfectly normal for simply stating position.

It would become:

Les amortisseurs sont sous la voiture.

Changes:

• L’amortisseur → Les amortisseurs
• est → sont

So:

• singular: L’amortisseur est sous la voiture.
• plural: Les amortisseurs sont sous la voiture.

Notice that sous la voiture does not change.

Yes. The apostrophe shows that a vowel was dropped in le.

So:

• le amortisseur becomes l’amortisseur

In careful writing, this apostrophe is required. You cannot write l amortisseur without it, and you cannot normally keep le before a vowel here.

It is a standard part of French spelling, not optional punctuation.