Je vais demander à Marie de m’aider.

Because aller + infinitive is a very common way to talk about the near future in French.

• je vais demander = I’m going to ask
• literally, vais comes from aller (to go), but here it does not mean physical movement

So this is the same idea as English I’m going to ask.

You could also say je demanderai, which is the simple future and means I will ask. Both are correct, but je vais demander often sounds more natural in everyday speech.

Because with demander, French often uses this pattern:

demander à quelqu’un de faire quelque chose
= to ask someone to do something

So in this sentence:

• à Marie = Marie is the person being asked

French needs that à here. You cannot normally say demander Marie de... in standard French.

Because after demander à quelqu’un, French uses de + infinitive to express the action you want that person to do.

Pattern:

demander à quelqu’un de + infinitive

So:

• demander à Marie de m’aider
• literally: ask Marie to help me

That de is required in this structure.

Because me becomes m’ before a vowel sound.

This is called elision.

• me aider → m’aider

French does this to make pronunciation smoother, just like:

• je aime → j’aime
• le ami → l’ami

So m’aider simply means to help me.

In French, object pronouns usually come before the verb they belong to.

So French says:

• m’aider = help me

where English says the pronoun after the verb: help me

This is normal in French infinitive structures:

• te voir = to see you
• nous aider = to help us
• lui parler = to speak to him/her

Marie is the person who is supposed to do the helping.

The structure tells you that:

• Je vais demander à Marie... = I’m going to ask Marie...
• ...de m’aider = ...to help me

So the meaning is:

• I will do the asking
• Marie will hopefully do the helping
• me / m’ refers to the person receiving the help

Yes. Demander can work in a few related ways:

• demander quelque chose = to ask for something
• demander à quelqu’un = to ask someone
• demander à quelqu’un de faire quelque chose = to ask someone to do something

Examples:

• Je demande de l’aide. = I’m asking for help.
• Je demande à Marie. = I’m asking Marie.
• Je demande à Marie de m’aider. = I’m asking Marie to help me.

So the exact meaning depends on what comes after demander.

Yes. That would also be correct.

The difference is mainly style and feel:

• Je vais demander à Marie de m’aider = I’m going to ask Marie to help me
• Je demanderai à Marie de m’aider = I will ask Marie to help me

In everyday spoken French, aller + infinitive is very common. The simple future (je demanderai) can sound a bit more formal, more definite, or simply more written, depending on context.

Because after demander, the normal construction is de + infinitive, not pour + infinitive.

So French says:

• demander à quelqu’un de faire quelque chose

not:

• demander à quelqu’un pour faire quelque chose

So de m’aider is the correct form here.

A rough pronunciation is:

zhuh vay duh-mahn-day ah mah-REE duh may-day

A few useful points:

• Je often sounds like zhuh
• vais sounds roughly like vay
• demander has a nasal sound in -man-
• m’aider sounds like may-day
• the final r of demander is pronounced, but softly in many accents

If you want a more accurate guide, the IPA is:

/ʒə vɛ d(ə)mɑ̃de a maʁi də mede/

It is neutral and completely natural.

Nothing in it is especially formal or especially casual. You could say it in normal conversation without any problem.

If you wanted to sound a little more formal, you might use je demanderai instead of je vais demander, but the original sentence is perfectly standard French.