Paghiamo cento euro.

Paghiamo is the 1st person plural form of the verb pagare (to pay) in the present indicative.

So it means we pay and, depending on context, it can also correspond to English we are paying.

The h is there to keep a hard g sound.

• pagare has a hard g, like the g in go
• Before i or e, Italian g normally becomes soft, like the j sound in English jam
• So Italian adds h to keep the hard sound: ghi

That is why it is paghiamo, not pagiamo.

Italian often leaves out subject pronouns because the verb ending already shows who is doing the action.

• paghiamo already tells you it means we pay
• So Paghiamo cento euro is completely natural

You can add noi for emphasis or contrast:

• Noi paghiamo cento euro, loro cinquanta.
  We pay one hundred euros, they pay fifty.

Cento is the number one hundred. Numbers do not usually change for plural in this kind of sentence.

So:

• cento euro = one hundred euros
• duecento euro = two hundred euros

You just use the number word as it is.

In Italian, euro normally stays the same in both singular and plural.

So:

• un euro
• due euro
• cento euro

Unlike English, Italian does not add -s, and unlike many Italian nouns, euro usually does not change ending in the plural.

No. After a number, you normally do not use an article.

So:

• paghiamo cento euro
• costa venti euro
• ho tre libri

This is similar to English: you say one hundred euros, not the one hundred euros, unless you specifically mean a particular set of euros in context.

The dictionary form is pagare, meaning to pay.

A few present-tense forms are:

• io pago = I pay
• tu paghi = you pay
• lui/lei paga = he/she pays
• noi paghiamo = we pay
• voi pagate = you all pay
• loro pagano = they pay

So paghiamo is just one conjugated form of pagare.

Yes. This is a very normal Italian word order:

• verb + amount

So Paghiamo cento euro sounds natural and straightforward.

Italian can sometimes move words around for emphasis, but this basic order is the most neutral one here.

Yes. The noi form can also be used as an imperative, meaning let’s ...

So depending on context:

• Paghiamo cento euro. = We pay one hundred euros.
• Paghiamo cento euro! = Let’s pay one hundred euros!

In your sentence, without special context, it will usually be understood as a statement.

A simple pronunciation guide is:

pa-GHYA-mo CHEN-to EU-ro

A few points:

• ghi sounds like a hard g
  • ya
• cento starts with a ch-like sound, roughly CHEN-to
• euro in Italian is usually pronounced something like EU-ro, with the first part sounding like eh-oo said smoothly

The stress is on:

• pa-GHIA-mo
• CHEN-to
• EU-ro

Yes, that is grammatically correct.

But in normal Italian, noi is often unnecessary because paghiamo already shows the subject. So:

• Paghiamo cento euro = more neutral and natural in many situations
• Noi paghiamo cento euro = more emphatic, contrastive, or explicit

For example, you might use noi if you are contrasting your group with another group.