Il faut tailler la haie avant que les invités arrivent.

Il faut is an impersonal expression meaning it is necessary or more naturally you have to / we have to / one must, depending on context.

The il here does not refer to a person or thing. It is just a grammatical subject required in French, like in il pleut (it is raining).

So:

• Il faut partir. = We have to leave / It is necessary to leave.
• Il faut tailler la haie. = The hedge needs to be trimmed / We have to trim the hedge.

It is one of the most common ways to express necessity in French.

After il faut, French normally uses an infinitive when talking about the action that is necessary.

So the structure is:

• Il faut + infinitive

Examples:

• Il faut manger. = You have to eat.
• Il faut attendre. = You have to wait.
• Il faut tailler la haie. = You have to trim the hedge.

If you want to say that a specific person must do something, French can also use:

• Il faut que + subject + verb

For example:

• Il faut que je parte. = I have to leave.
• Il faut que nous taillions la haie. = We have to trim the hedge.

Tailler means to cut back, trim, or prune, depending on the context.

With la haie (the hedge), tailler la haie specifically means:

• to trim the hedge
• to cut back the hedge

French uses tailler very naturally for plants, hedges, shrubs, and sometimes trees.

So although tailler can have other meanings in other contexts, here it clearly means trim/cut back.

French uses articles much more often than English does. Where English might say trim hedge only in a very reduced style, normal English says trim the hedge, and French also normally needs the article:

• la haie = the hedge

So tailler la haie is the normal way to say trim the hedge.

In French, bare nouns without an article are much less common than in English.

Avant que means before when it is followed by a full clause with its own subject and verb.

Here, the second part is:

• les invités arrivent = the guests arrive

So you need:

• avant que les invités arrivent

Compare that with avant de, which is used before an infinitive, usually when the subject stays the same:

• Il faut tailler la haie avant de partir.
  = We have to trim the hedge before leaving.

But if you want to say before the guests arrive, you need a separate subject (les invités), so French uses avant que.

After avant que, French normally uses the subjunctive, not the future.

So:

• avant que les invités arrivent

is grammatically expected.

This can feel strange to English speakers, because English often uses a present form after before too, but French is following a specific rule: avant que triggers the subjunctive.

Important detail: For ils arrivent, the present subjunctive and the present indicative look the same in writing and sound the same in speech:

• Indicative: ils arrivent
• Subjunctive: qu’ils arrivent

So the form looks ordinary, but after avant que, it is understood as subjunctive.

French often uses the subjunctive after expressions that involve anticipation, uncertainty, emotion, necessity, or something not yet realized.

With avant que, the action after it has not happened yet at the moment being discussed. That is why French treats it as something pending or not yet actualized, and uses the subjunctive.

So in:

• Il faut tailler la haie avant que les invités arrivent

the guests have not arrived yet. Their arrival is still in the future relative to the hedge-trimming.

Yes. Very often, especially in more careful or formal French, you may see:

• avant que les invités n’arrivent

That ne is called the explétif ne. It does not make the sentence negative.

So these two mean the same thing:

• avant que les invités arrivent
• avant que les invités n’arrivent

The version without ne is very common in everyday speech and informal writing. The version with ne is more formal or traditional.

Les invités means the guests.

French often uses the definite article where English does too, but it is worth noticing that les does not always have to mean a very specific, already-mentioned group in the same way English sometimes does. It can simply mean the expected set of guests in the situation.

So:

• les invités = the guests

If you said des invités, that would mean some guests, which is less natural here if you mean the guests who are coming.

Yes, invités is the masculine plural form.

In French, a mixed group or a group of unknown gender normally uses the masculine plural:

• les invités

If the guests were all women, you would say:

• les invitées

In speech, the difference is often not heard clearly, but in writing it matters.

A careful everyday pronunciation would be roughly:

il fo ta-ye la è a-van ke lez-in-vi-tay a-riv

A few useful points:

• Il faut: the l in il is usually heard, but lightly.
• tailler: sounds like ta-ye.
• haie: the h is silent; haie sounds like è.
• les invités: there is a liaison, so it sounds like lez-invités.
• arrivent: the -ent ending is silent.

So the end sounds like:

• avant que lez-invités arrivent

Yes, that is possible, but it is slightly different in tone.

• Il faut tailler la haie... = It’s necessary to trim the hedge / We have to trim the hedge
• On doit tailler la haie... = We have to trim the hedge

Il faut sounds more impersonal and objective: it presents the action as necessary. On doit sounds more directly like we have to.

Both are natural, but il faut is especially common when giving a general necessity or practical requirement.