הם דיברו על נישואין.

A common pronunciation is:

hem dibru al nisu'in

A rough breakdown:

• הם = hem
• דיברו = di-BRU
• על = al
• נישואין = ni-su-IN

The stress is usually on the last syllable in דיברו and נישואין.

הם means they.

It is the 3rd person plural pronoun, usually for:

• a masculine plural group, or
• a mixed-gender group

In formal Hebrew, an all-female group would be הן, but in everyday speech many speakers use הם very broadly.

דיברו is the past tense, 3rd person plural form of the verb לדבר, meaning to speak / to talk.

So:

• הוא דיבר = he spoke / talked
• היא דיברה = she spoke / talked
• הם דיברו = they spoke / talked

The ending -ו is a very common past-tense plural ending in Hebrew.

Good question. In Hebrew, the verb form often already tells you the subject, so דיברו על נישואין can by itself mean They talked about marriage.

Adding הם can:

• make the sentence clearer
• add emphasis
• make the subject more explicit in context

So both are possible:

• דיברו על נישואין = They talked about marriage
• הם דיברו על נישואין = They talked about marriage / They were the ones talking about marriage

Because לדבר על means to talk about.

So:

• דיברו על נישואין = they talked about marriage

This is a very common pattern:

• לדבר על משהו = to talk about something

Compare:

• לדבר עם מישהו = to talk with someone
• לדבר אל מישהו = to speak to someone
  (more formal or directional)

נישואין means marriage or marriage/wedding in a formal or general sense, depending on context.

In this sentence, it most naturally means:

• marriage as a topic, or
• getting married

So הם דיברו על נישואין usually means they were discussing the subject of marriage, not necessarily one specific wedding event.

Because נישואין is one of those Hebrew nouns that has a plural-looking form but often refers to a single concept.

This is normal. In many contexts, it behaves like a set or institution rather than a simple countable noun.

Also, you may also see נישואים, which is a very common modern form of the same word.
Very roughly:

• נישואין = a bit more formal/literary
• נישואים = very common in everyday modern Hebrew

Because the sentence is talking about marriage in general, not the marriage or the wedding.

So:

• על נישואין = about marriage
• על הנישואין = about the marriage / about the wedding

Adding ה־ makes the noun definite.

This is a very useful distinction.

• נישואין usually refers to marriage as an institution, legal/religious union, or the general concept of marrying.
• חתונה usually means wedding, especially the event or ceremony.

So:

• הם דיברו על נישואין = they talked about marriage
• הם דיברו על חתונה = they talked about a wedding / the wedding

Sometimes the meanings can overlap a little in context, but that is the basic difference.

In formal Hebrew, you would use הן instead of הם:

הן דיברו על נישואין.

Interestingly, the verb דיברו stays the same here in the past plural.

So:

• הם דיברו = they spoke (masculine or mixed)
• הן דיברו = they spoke (feminine, formal)

In everyday spoken Hebrew, many people use הם very often even when referring to women, depending on style and context.