Je cherche mes clés dans le tiroir pendant que Marie prépare le café.

Because chercher in French takes a direct object. You say:

• chercher quelque chose = to look for something

So:

• Je cherche mes clés = I’m looking for my keys

English uses look for, but French does not need a preposition here.

In French, a possessive word like mon, ma, mes, ton, ses, nos already replaces the article.

So you say:

• mes clés = my keys

not:

• les mes clés

This works the same way with other possessives:

• mon livre = my book
• sa voiture = his/her car
• nos amis = our friends

Clés is the plural of clé, meaning key.

• clé = key
• clés = keys

The s marks the plural. The accent in clé is part of the normal spelling. You may also sometimes see clef, which is another correct spelling of key, though clé is very common in modern usage.

In this sentence, dans le tiroir most naturally means that the search is happening in the drawer—in other words, you are looking for the keys there.

So the idea is:

• I’m looking for my keys in the drawer

French often leaves this kind of attachment to context, just like English does. No one would think you are physically in the drawer.

Le tiroir means the drawer, usually a specific drawer that is known or understood from context.

• dans le tiroir = in the drawer
• dans un tiroir = in a drawer

If the speaker has a particular drawer in mind, le is natural. If the drawer is not specific or not yet identified, un would be more likely.

Pendant que means while or during the time that.

It introduces a clause with a verb and shows that two actions happen at the same time:

• Je cherche mes clés pendant que Marie prépare le café.
• I’m looking for my keys while Marie is making the coffee.

A useful contrast:

• pendant
  • noun
• pendant que
  • clause with a verb

Examples:

• pendant le film = during the movie
• pendant que je travaille = while I’m working

French often uses the present tense for actions happening right now, just like English can in sentences such as I’m looking or Marie is making.

So:

• je cherche = I look / I’m looking
• Marie prépare = Marie prepares / Marie is preparing

In context, this present tense is understood as an action in progress.

Because the verb is préparer and the subject is Marie, which is third person singular.

Present tense of préparer:

• je prépare
• tu prépares
• il/elle/on prépare
• nous préparons
• vous préparez
• ils/elles préparent

Since Marie is like elle, the correct form is prépare.

Both can exist in French, but they do not feel exactly the same.

• préparer le café often means prepare the coffee in a general, familiar situation — for example, the coffee for breakfast, the usual coffee everyone knows about
• préparer du café emphasizes some coffee as a substance

So in this sentence, Marie prépare le café sounds very natural if the coffee is part of an understood situation.

Compare:

• Marie prépare le café = Marie is making the coffee
• Marie prépare du café = Marie is making some coffee

Usually, no comma is required in a sentence like this.

So this is normal:

• Je cherche mes clés dans le tiroir pendant que Marie prépare le café.

A comma might be added for style or emphasis, but in ordinary French it is often omitted when the sentence flows naturally.

Because Marie is a proper name, and in standard French proper names usually do not take an article.

So:

• Marie prépare le café

not normally:

• la Marie prépare le café

In some regional or informal varieties, you may hear an article before a name, but that is not the standard form taught to learners.

All three can sometimes be translated as while, but the nuance is different.

• pendant que = mainly shows that two actions happen at the same time
• alors que = often introduces contrast, something like whereas or while
• tandis que = can also suggest contrast, and can sound a little more formal

In your sentence, pendant que is the most straightforward choice because it simply describes simultaneous actions.

A simple pronunciation guide is:

Je cherche mes clés dans le tiroir pendant que Marie prépare le café
roughly: zhuh shersh may clay dahn luh tee-rwahr pahn-dahn kuh mah-ree pray-pahr luh kah-fay

A few helpful notes:

• je sounds like zhuh
• cherche has the sh sound in the middle
• clés sounds like clay
• dans has a nasal vowel, so the n is not fully pronounced like in English
• Marie is mah-ree
• café ends with a clear ay sound

Yes. That would be correct and a bit more explicit about the action being in progress.

• Je cherche mes clés = I’m looking for my keys
• Je suis en train de chercher mes clés = I’m in the middle of looking for my keys

The version in your sentence is more natural and more common in everyday French unless you specifically want to stress the ongoing action.