La commande est sur le site.

In French, a singular countable noun usually needs an article or another determiner.

So French normally says:

• la commande = the order
• une commande = an order

Using commande by itself would sound incomplete in a basic sentence like this.

Also, commande is feminine singular, which is why the article is la.

You know it here because the sentence uses la, the feminine singular definite article.

French nouns have grammatical gender, so you have to learn each noun with its article:

• la commande
• le site

There is not always a logical reason from an English point of view, so it is best to memorize the noun together with le or la.

Est is the third-person singular form of the verb être (to be) in the present tense.

So:

• je suis = I am
• tu es = you are
• il / elle est = he / she is

Since la commande is a singular subject, French uses est.

French often uses sur with websites, meaning something like on the site or on the website.

So:

• sur le site = on the site / on the website

Using dans le site is usually not the normal choice for this idea. Dans suggests being inside something in a more physical or internal sense, while sur is the standard preposition for websites and many surfaces.

Yes. In this sentence, site is masculine, so French uses le.

That gives:

• le site = the site

If it were feminine, you would see la site, but that is not correct.

Because French contractions happen only with certain prepositions.

The most important ones are:

• à + le = au
• à + les = aux
• de + le = du
• de + les = des

But sur does not contract with le.

So you say:

• sur le site

not a shortened form.

It can mean both, depending on context.

Common meanings include:

• a website
• a site in the sense of a location or place
• sometimes a work site, historical site, industrial site, and so on

So sur le site could mean on the website or sometimes on the site in a physical sense. Context tells you which meaning is intended.

Yes, that is possible.

• La commande est sur le site is simple and direct.
• La commande se trouve sur le site can sound a bit more explicit, like The order is located on the site.

In many cases, est is the most natural and straightforward choice.

There are a few common ways:

• La commande est sur le site ?
  Informal, very common in speech.

• Est-ce que la commande est sur le site ?
  Very common and clear.

• La commande est-elle sur le site ?
  More formal, with inversion.

All three can mean the same thing.

A simple pronunciation guide is:

la koh-mahnd eh sur luh seet

A few points:

• commande ends with a pronounced d sound.
• est is usually pronounced eh here.
• site sounds like seet.
• In normal speech, le can sound very light.

A rough IPA version is:

/la kɔ.mɑ̃d ɛ syʁ lə sit/

Yes, there can be one between est and sur.

Many speakers pronounce:

• est sur with a t sound linking the words

So it can sound like:

• eh-t-sur

This liaison is normal and natural here.

There is no special contraction or major sound change in sur le site.