Ha sposato la sua amica.

It is the passato prossimo, a very common Italian past tense.

It is formed with:

• ha = the auxiliary verb avere
• sposato = the past participle of sposare

So:

• ha sposato = married / has married, depending on context in English.

Italian often leaves out subject pronouns when they are not needed.

The verb ha already tells you the subject is:

• he
• she
• sometimes it
• or formal you

So Italian does not need to say lui or lei unless the speaker wants emphasis or contrast.

It could mean either one.

This sentence is gender-ambiguous:

• ha does not show whether the subject is male or female
• sua can mean his or her

So without more context, Ha sposato la sua amica could mean:

• He married his female friend
• She married her female friend

Context normally makes it clear.

Because the possessive adjective agrees with the thing possessed, not with the possessor.

Here the possessed noun is:

• amica = feminine singular

So the possessive must also be feminine singular:

• sua amica

Compare:

• il suo amico = his/her male friend
• la sua amica = his/her female friend

Because in Italian, possessives are usually used with the definite article.

So Italian says:

• la sua amica
• literally something like the his/her friend

This is normal Italian structure.

A common exception is with singular close family members:

• mia madre
• tuo fratello
• sua sorella

But amica is not a family term, so the article stays:

• la sua amica

Because with avere, the past participle usually does not agree with the subject.

So you get:

• Lui ha sposato la sua amica
• Lei ha sposato la sua amica

In both cases, it stays sposato.

Agreement with the subject is much more typical with essere:

• Lei è andata
• Lui è andato

Because that is a slightly different structure.

• sposare qualcuno = to marry someone
• sposarsi con qualcuno = to get married to someone

So:

• Ha sposato la sua amica = He/She married his/her female friend
• Si è sposato/a con la sua amica = He/She got married to his/her female friend

They refer to the same kind of event, but the grammar is different.

Formally, it is built with has + past participle, yes.

But in actual translation, Italian passato prossimo often corresponds to the English simple past:

• Ha sposato la sua amica = He/She married his/her friend

Sometimes English has married is possible, but very often married is the more natural translation.

Yes, in some contexts it can be ambiguous.

Very often, the natural reading is that sua refers to the subject:

• He married his female friend
• She married her female friend

But context might show a different possessor. If Italian speakers want to be very clear, they can use:

• l'amica di lui
• l'amica di lei

Those are more explicit, though often less natural unless clarification is needed.

Not necessarily.

amica normally means female friend.

If you specifically mean girlfriend in the romantic sense, Italian usually uses a clearer word such as:

• fidanzata
• sometimes ragazza, depending on context

So la sua amica should normally be understood as his/her female friend, not automatically girlfriend.

Yes, but context matters.

Besides to marry someone, sposare can also mean:

• to support
• to embrace
• to adopt an idea or cause

For example:

• sposare una teoria = to embrace a theory

Also, in some contexts, a priest or mayor can sposare a couple, meaning to officiate the wedding.

But in Ha sposato la sua amica, the normal meaning is simply that the subject married his/her female friend.