Bonsoir !

It’s pronounced roughly bohn-SWAHR.

A more precise French pronunciation is /bɔ̃.swaʁ/:

• bon has a nasal vowel, so the n is not fully pronounced like in English
• soir sounds like swahr
• the final r is the French r, made farther back in the throat than an English r

If you say bohn-swar, most people will still understand you.

Use Bonsoir in the evening.

A simple learner-friendly rule is:

• Bonjour = during the day
• Bonsoir = from early evening onward

The exact time can depend on context and season, but Bonsoir is the normal greeting once it feels like evening.

Not usually.

Bonsoir is mainly a greeting, like good evening.

If you are leaving and want to say good night, French usually uses:

• Bonne nuit = good night

So:

• arriving in the evening: Bonsoir
• going to bed / ending the night: Bonne nuit

Because it’s a fixed French expression.

In greetings, French often combines words into one standard form:

• bonjour
• bonsoir

Even though it historically comes from bon + soir, the normal modern spelling is bonsoir as one word.

Because soir is a masculine noun in French.

• bon = masculine form of good
• bonne = feminine form of good

Since soir is masculine, French uses:

• bon soir → written as bonsoir

Compare:

• bon matin would be masculine in structure, though French normally does not use this as a standard greeting
• bonne nuit uses bonne because nuit is feminine

Yes. Bonsoir works for:

• one person
• several people
• formal situations
• informal situations

Unlike some other French expressions, it does not change depending on who you are talking to.

No. It’s not required.

You can write:

• Bonsoir
• Bonsoir !

The exclamation mark simply makes it feel a little more lively or friendly. In texting or casual writing, both are common.

No, Bonsoir can stand on its own.

But you can add something after it if you want:

• Bonsoir, Madame.
• Bonsoir, Pierre.
• Bonsoir à tous.

On its own, Bonsoir ! is already a complete greeting.

Sometimes, yes, but its main use is as a greeting.

In some situations, especially formal ones, someone may say Bonsoir at the moment of departure in the evening. But for learners, the safest rule is:

• Bonsoir = hello in the evening
• Bonne soirée = have a good evening
• Bonne nuit = good night

So if you are leaving, Bonne soirée is often the more natural choice.

They are used differently:

• Bonsoir = good evening as a greeting
• Bonne soirée = have a nice evening when leaving

For example:

• when you arrive at a dinner: Bonsoir !
• when you leave the dinner: Bonne soirée !

That difference is very useful to remember.

Usually, no.

In normal French, greetings like bonjour and bonsoir are generally written with a lowercase letter, unless they start the sentence:

• Bonsoir !
• Je lui ai dit bonsoir.

So in your example, it is capitalized because it begins the sentence.