Il socio firma il contratto.

Because il is the masculine singular definite article, meaning the.

In this sentence:

• il socio = the partner/member/shareholder
• il contratto = the contract

Italian normally uses articles before nouns much like English does, and here both nouns are:

• masculine
• singular
• beginning with a consonant sound that takes il

So il appears once before each noun because each noun needs its own article.

Here, firma is a verb: the third-person singular present tense of firmare, meaning to sign.

So:

• firmare = to sign
• firma = he signs / she signs / it signs

In this sentence, il socio is singular, so the verb is also singular:

• Il socio firma = The partner signs

A learner may notice that firma can also be a noun in other contexts, such as signature or brand/company name, but in this sentence it is clearly a verb because of the structure:

• subject + verb + object

In Italian, the verb ending often already tells you the subject, so subject pronouns are often omitted.

The form firma means:

• he signs
• she signs
• it signs
• or you sign in the formal singular (Lei firma)

But here the subject is explicitly stated as il socio, so there is no need for a separate pronoun.

Italian commonly does this:

• Il socio firma. rather than
• Lui firma.

The noun itself tells you who is doing the action.

Because il contratto is the direct object of the verb firma.

In English, sign takes a direct object directly:

• sign the contract

Italian works the same way:

• firmare il contratto

No preposition is needed. So:

• Il socio firma il contratto = subject + verb + direct object

If a preposition were added, the meaning or grammar would change.

The normal, neutral word order is:

• Il socio = subject
• firma = verb
• il contratto = object

So:

• Il socio firma il contratto.

This is the most straightforward order and the best one for learners to use.

However, Italian word order is more flexible than English. In some contexts, you may also hear:

• Il contratto lo firma il socio.
• Firma il contratto il socio.

These versions change the emphasis or sound more marked. For a basic statement, Il socio firma il contratto is the standard choice.

Yes, socio is a masculine singular noun.

That is why it takes:

• il socio

The feminine singular form is usually:

• la socia

So you could say:

• Il socio firma il contratto.
• La socia firma il contratto.

Plural forms:

• i soci = the male/mixed partners or members
• le socie = the female partners or members

Yes. The Italian present tense often covers several meanings that English may express in different ways.

Firma can mean:

• signs
• is signing
  depending on context

So Il socio firma il contratto could mean:

• The partner signs the contract
• The partner is signing the contract

Without more context, the Italian present tense is somewhat flexible. English often forces you to choose between simple present and present continuous, but Italian often does not.

A simple approximate pronunciation for an English speaker is:

eel SOH-cho FEER-ma eel kon-TRAT-to

A few useful details:

• il sounds roughly like eel, but shorter
• socio has cio pronounced like cho
• firma has a rolled or tapped r if possible
• contratto has double tt, so the t sound is held a little longer than in English
• the stress falls on:
  • SO in socio
  • FIR in firma
  • TRAT in contratto

Yes, but the meaning changes.

• Il socio firma il contratto = The partner signs the contract
• Un socio firma un contratto = A partner signs a contract

So the difference is definite versus indefinite:

• il = the
• un = a

The original sentence sounds like we are talking about a specific partner and a specific contract, or about them in a general-but-defined context.

Not always. Depending on context, socio can mean things like:

• partner
• associate
• member
• shareholder

So even if the basic meaning has already been given, a learner should know that the exact English translation depends on the situation.

For example:

• in a company context, it might mean partner or shareholder
• in a club or organization, it might mean member

The grammar of the sentence stays the same even if the best English word changes with context.