لازم است که قبل از شام میز را آماده کنیم.

لازم means necessary, and است means is. So لازم است literally means is necessary or more naturally it is necessary.

Persian often uses this kind of impersonal expression without a dummy subject. English needs it in it is necessary, but Persian does not. So لازم است is complete on its own.

Here, که introduces the following clause, like English that in it is necessary that...

So:

لازم است که ... = it is necessary that ...

Yes, که can often be omitted here:

لازم است قبل از شام میز را آماده کنیم

Both are correct. Keeping که can make the sentence feel a bit clearer or slightly more formal.

قبل از is a fixed expression meaning before.

• قبل = before
• از = from/of

Together, قبل از شام means before dinner.

This pattern is very common in Persian:

• قبل از کلاس = before class
• قبل از خواب = before sleep / before going to bed

را marks a specific direct object.

So in میز را, the speaker means a particular table, basically the table.

A native English speaker can think of را as a marker that says, this noun is the direct object, and it is specific/known.

In spoken Persian, را is often pronounced رو or just -o:

• میز را → میزو

آماده کنیم is a compound verb:

• آماده = ready
• کنیم = we do / we make

So literally it is make ready.

This is very common in Persian: an adjective or noun combines with کردن to form a verb-like meaning.

Here, میز را آماده کنیم means get the table ready or prepare the table.

Depending on context, English might translate it as set the table, but Persian also has more specific expressions such as میز را بچینیم, which is closer to set the table.

Because after expressions like لازم است and باید, Persian usually uses the subjunctive form.

So:

• کنیم = that we do / that we prepare
• می‌کنیم = we do / we are doing

In this sentence, the idea is not describing an action that is happening now. It expresses necessity or what should be done, so the subjunctive کنیم is the correct form.

The ending -یم shows the subject is we.

So:

• کنم = I do
• کنی = you do
• کند = he/she/it does
• کنیم = we do
• کنید = you (plural/formal) do
• کنند = they do

Because the verb ending already tells you the subject, Persian often leaves out the pronoun ما (we).

Yes, you could say:

لازم است که ما قبل از شام میز را آماده کنیم

But ما is usually omitted unless you want emphasis or contrast. Since کنیم already means we, the pronoun is not necessary.

Persian commonly drops subject pronouns when the verb ending makes the subject clear.

The verb usually stays near the end, but the other parts are somewhat flexible.

Your sentence is:

لازم است که قبل از شام میز را آماده کنیم

You could also say:

لازم است که میز را قبل از شام آماده کنیم

Both are natural. The first version emphasizes the time phrase a bit earlier; the second puts the object earlier. Persian allows this kind of flexibility more than English does, as long as the sentence remains clear and the verb comes at the end.

A careful pronunciation is:

lāzem ast ke ghabl az shām miz râ āmāde konim

In everyday spoken Persian, it often sounds more like:

lāzeme ke ghabl az shām mizo āmāde konim

A few common spoken changes are:

• لازم است → لازمه
• را → رو / -o

So learners will often hear something closer to the colloquial version in conversation.

Yes. A very common alternative is:

باید قبل از شام میز را آماده کنیم

This also means that it is necessary to do it.

A rough comparison:

• لازم است که ... = it is necessary that ...
• باید ... = must / have to / should

In many everyday situations, باید is more common and direct. لازم است can sound a little more formal or more explicitly like a statement of necessity.