Je viens de conseiller à Marie de sortir un instant, car la peinture fraîche peut être toxique.

In this sentence, venir de + infinitive is an idiom that means to have just done something.

So:

• Je viens de conseiller... = I have just advised...

It does not literally mean that the speaker is physically coming from somewhere.

This is called the recent past in French:

• Je viens de manger = I’ve just eaten
• Elle vient d’arriver = She has just arrived

So Je viens de conseiller à Marie de sortir un instant means the advice was given very recently.

Because conseiller often works with this pattern:

• conseiller à quelqu’un de faire quelque chose

That means:

• to advise someone to do something

So here:

• à Marie = to Marie
• de sortir = to go out / to step outside

The whole structure is:

• conseiller à Marie de sortir = advise Marie to go out

French does not usually say this the same way English does. English uses advise someone to do something, but French often uses:

• advise to someone of doing something
• in proper French structure: conseiller à quelqu’un de faire quelque chose

After conseiller à quelqu’un, French uses de + infinitive before the action being advised.

So:

• conseiller à Marie de sortir
• conseiller à Paul d’attendre
• conseiller aux enfants de rentrer

You cannot normally drop the de here.

This is just part of the verb pattern learners need to remember:

• conseiller à quelqu’un de + infinitive

Yes. That would also be correct.

The difference is:

• J’ai conseillé à Marie de sortir = I advised Marie to go out
• Je viens de conseiller à Marie de sortir = I have just advised Marie to go out

So venir de + infinitive adds the idea of just now or a moment ago.

Sortir un instant means to go out for a moment or to step outside briefly.

• sortir = to go out / to leave
• un instant = a moment

In this context, it probably means Marie should leave the room or area briefly because of the fresh paint.

A very natural English translation would be:

• to step out for a moment

In French, most adjectives come after the noun.

So:

• la peinture fraîche = the fresh paint

That is the normal order here.

Some adjectives do come before the noun, but frais / fraîche usually comes after when it means something like fresh, new, or in this case still fresh/wet.

So la peinture fraîche is the expected phrasing.

Because peinture is a feminine singular noun.

French adjectives usually agree with the noun they describe.

Here:

• peinture = feminine singular
• so the adjective must also be feminine singular: fraîche

The forms are:

• masculine singular: frais
• feminine singular: fraîche
• masculine plural: frais
• feminine plural: fraîches

So:

• un pain frais = a fresh loaf of bread
• une peinture fraîche = fresh paint

Some French adjectives have the same form in the masculine and feminine.

Toxique is one of them.

So you get:

• un produit toxique
• une peinture toxique

The spelling stays the same in both singular forms.

Only the plural changes:

• des produits toxiques
• des peintures toxiques

No. This is an important difference.

In your sentence:

• peut être = can be

Here:

• peut = can / may
• être = to be

So:

• la peinture fraîche peut être toxique = fresh paint can be toxic

But peut-être with a hyphen is a different expression:

• peut-être = perhaps / maybe

For example:

• Peut-être qu’elle sortira = Maybe she will go out

So:

• peut être = can be
• peut-être = maybe

Both can mean because, but they are not used in exactly the same way.

In this sentence:

• car la peinture fraîche peut être toxique

Car introduces an explanation or justification. It is often a bit more formal or written-sounding than parce que.

So this sentence could also be written with parce que:

• ... parce que la peinture fraîche peut être toxique

But car works very naturally in a sentence like this, especially after a comma.

A useful difference:

• car often sounds like for / because, you see
• parce que is the more common everyday because

You would use lui.

So:

• Je viens de lui conseiller de sortir un instant.

Here:

• lui = to her / to him

That is because Marie is an indirect object after à.

Compare:

• Je parle à Marie → Je lui parle
• Je conseille à Marie de sortir → Je lui conseille de sortir

So à Marie becomes lui.

It can mean either, depending on context.

Sortir often means:

• to go out
• to go outside
• to leave a place

In this sentence, because of the fresh paint, it most likely means:

• to step out of the room/area for a moment
• possibly to go outside briefly

French leaves that a little open, and the exact meaning comes from the situation.