Il materiale preparatorio aiuta l'interprete di conferenza.

Because materiale is a masculine singular noun in Italian, so it takes the masculine singular article il.

• il materiale = the material
• i materiali = the materials

This can feel surprising to English speakers because material in English does not have grammatical gender, but in Italian every noun does.

Materiale preparatorio means preparatory material or preparation material.

Here, preparatorio is an adjective describing materiale:

• materiale = material
• preparatorio = preparatory

In Italian, adjectives often come after the noun, so materiale preparatorio literally looks like material preparatory to an English speaker.

In Italian, adjectives usually come after the noun they describe, especially when they are more descriptive or technical.

So:

• materiale preparatorio = preparatory material

This is the normal, natural order in Italian. English usually puts adjectives before the noun, but Italian often puts them after.

L' is a shortened form of the definite article used before a word that begins with a vowel.

• il interprete would sound awkward and is not correct
• l'interprete is the correct form

This is called elision. The vowel in the article drops before another vowel.

It can be either masculine or feminine, depending on the person.

• l'interprete = the interpreter
• it may refer to a man or a woman

If you need to make the gender clearer in some contexts, the article or other words in the sentence may help:

• un interprete bravo = a good male interpreter
• un'interprete brava = a good female interpreter

In your sentence, l'interprete by itself could refer to either.

Di conferenza means of conference or more naturally in English, conference.

So:

• interprete di conferenza = conference interpreter

Italian often uses di + noun where English uses a noun as an adjective:

• sala da pranzo = dining room
• macchina da scrivere = typewriter
• interprete di conferenza = conference interpreter

Because interprete di conferenza is a fixed and natural way to say conference interpreter in Italian.

Very roughly:

• di often expresses type, category, or association
• da often suggests purpose or use

Here, the idea is that the interpreter works in the field or context of conferences, so di conferenza is the normal expression.

Aiuta is the third person singular present tense of the verb aiutare, meaning to help.

So:

• io aiuto = I help
• tu aiuti = you help
• lui/lei aiuta = he/she helps

In this sentence, the subject is Il materiale preparatorio, which is singular, so the verb must also be singular:

• Il materiale preparatorio aiuta... = The preparatory material helps...

Because aiutare in Italian normally takes a direct object, while in English help can be used with or without to, depending on the structure.

So Italian says:

• aiutare qualcuno = to help someone

That is why you get:

• Il materiale preparatorio aiuta l'interprete di conferenza

There is no need for a preposition before l'interprete.

The subject is Il materiale preparatorio.

That is the thing doing the action:

• Il materiale preparatorio = the preparatory material

The verb is aiuta The object is l'interprete di conferenza

So the structure is:

• Il materiale preparatorio = subject
• aiuta = verb
• l'interprete di conferenza = object

Yes. That would mean The preparatory materials help the conference interpreter.

Notice the changes:

• Il materiale → I materiali
• preparatorio → preparatori
• aiuta → aiutano

Everything has to agree in number:

• singular: Il materiale preparatorio aiuta
• plural: I materiali preparatori aiutano

A simple pronunciation guide is:

eel mah-teh-RYAH-leh preh-pah-rah-TOH-ryoh ah-YOO-tah leen-tehr-preh-teh dee kon-feh-REN-tsah

A few helpful points:

• gli is not present here, so this sentence is relatively straightforward
• ci and ce are not present either
• conferenza has the stress on ren
• aiuta has the stress on yu

A more natural chunking is:

• Il materiale preparatorio
• aiuta l'interprete di conferenza

Yes, it is grammatical and natural, especially in a professional or educational context.

It sounds like the kind of sentence you might find in:

• a textbook
• a training manual
• a description of conference interpreting

It has a slightly formal or technical tone because of expressions like materiale preparatorio and interprete di conferenza.