Marie choisit un vernis simple pour ses ongles, mais elle ne met presque jamais de parfum au travail.

Choisit is the 3rd-person singular present tense of choisir. The subject is Marie, so French uses elle choisit.

By contrast, choisi is usually the past participle, as in Marie a choisi.

The sentence is in the present indicative. In this kind of context, French often uses the present to describe habits, usual behavior, or general facts, not just what is happening right now.

So the sentence suggests this is the kind of choice Marie typically makes, and that she almost never wears perfume at work.

Here, vernis means nail polish.

By itself, vernis can mean varnish, polish, or lacquer depending on the context. Because the sentence says pour ses ongles, it is clearly referring to nail polish. French often shortens vernis à ongles to simply vernis when the context is obvious.

Un vernis treats it as one item / one type / one choice of polish.

Du vernis would refer more to nail polish as an uncountable substance, like some nail polish in general.

So here, un vernis simple fits because Marie is choosing a particular polish.

The position of simple changes the nuance.

• un vernis simple = a simple/plain nail polish
• un simple vernis = just a nail polish, a mere nail polish

So the sentence uses un vernis simple because it is describing the style of the polish, not minimizing what it is.

It does agree with vernis, but simple has the same written form in both the masculine singular and the feminine singular.

Since vernis is masculine singular, the adjective is still simple.

If it were plural, you would write simples.

Pour ses ongles literally means for her nails.

With products like cosmetics or care items, French often uses pour to show what something is intended for. Here, it tells you what the polish is for.

It is a natural way to connect the product to the body part it is used on.

Because ongles is plural.

French possessive adjectives agree with the thing possessed, not with the person who owns it.

So:

• son ongle = his/her nail
• ses ongles = his/her nails

Even though Marie is one person, she has more than one nail, so French uses ses.

Literally, mettre means to put or to put on.

In this context, mettre du/de parfum means to wear perfume or to apply perfume. French often uses mettre for things like clothes, makeup, and fragrance.

So this is very natural French.

After a negative structure, French usually changes du / de la / des to de / d'.

That is why you get:

• Elle met du parfum.
• Elle ne met jamais de parfum.

In this sentence, ne ... presque jamais works like a near-negative expression, so de parfum is the normal form.

It means almost never.

The structure goes around the conjugated verb:

• elle ne met presque jamais

So:

• ne comes before the verb
• presque jamais comes after the verb

Together, they express something that happens very rarely.

Because French normally needs an explicit subject for each new clause with a conjugated verb.

So after mais, you start a new clause:

• Marie choisit...
• mais elle ne met...

In English, repeating the subject can sometimes feel optional, but in French it is usually required.

Because à + le contracts to au.

So:

• à + le = au
• à + les = aux

That is why French says au travail.

Here, au travail means at work or in the workplace.