כשהמורה מדברת, צריך לשתוק.

It is made of two parts:

• כש־ = when / while
• המורה = the teacher

So כשהמורה means when the teacher...

In Hebrew, short words like כש־ are often attached directly to the next word instead of being written separately.

Because מורה can mean either male teacher or female teacher in unpointed Hebrew spelling.

The spelling המורה is the same for both:

• the male teacher
• the female teacher

What tells you the gender here is the verb מדברת, which is feminine singular. So in this sentence, the teacher is female.

Because it has to agree with המורה as understood here: the female teacher.

מדברת is the feminine singular present-tense form of לדבר = to speak / to talk.

If the teacher were male, you would normally get:

• כשהמורה מדבר, צריך לשתוק.

So:

• מדברת = a woman is speaking
• מדבר = a man is speaking

It can mean either, depending on context.

Hebrew present tense often covers both:

• speaks
• is speaking

In this sentence, because of כש־ and the situation being described, English usually understands it as when the teacher is speaking.

So Hebrew does not always force the same distinction that English does between simple present and present continuous.

Here צריך means something like:

• one must
• you have to
• you should
• it is necessary to

So צריך לשתוק means it is necessary to be quiet / one must keep quiet.

The exact English translation depends on tone. In a classroom rule, it often feels like you have to be quiet or you should be quiet.

This is very common in Hebrew.

When Hebrew makes a general statement with צריך + infinitive, it often uses the masculine singular form by default, even when no specific male person is being talked about.

So צריך לשתוק is an impersonal expression meaning something like one must be quiet.

If you were speaking directly to someone, the form would change:

• to a woman: את צריכה לשתוק
• to a man: אתה צריך לשתוק
• to a group: אתם צריכים לשתוק

But in a general rule, צריך לשתוק is normal.

Because Hebrew often leaves the subject out in general statements.

English may need something like:

• you
• one
• people
• it is necessary

Hebrew can simply say צריך לשתוק and let the listener understand that it means a general obligation.

So this is not incomplete Hebrew. It is a normal impersonal construction.

לשתוק is the infinitive, meaning to be quiet / to keep silent / to shut up.

The ל־ is the normal marker for many Hebrew infinitives, similar to English to in to speak, to sit, to be quiet.

So:

• לשתוק = to be silent / to keep quiet

In this sentence, צריך לשתוק = must be quiet.

Yes. You can also say:

• צריך לשתוק כשהמורה מדברת.

That has the same basic meaning: When the teacher is speaking, you must be quiet.

Both orders are natural. The version with the when clause first can sound a little more like stating a rule up front.

The comma is natural and standard here because the sentence begins with a subordinate clause:

• כשהמורה מדברת = when the teacher is speaking

Then the main clause comes after it:

• צריך לשתוק = one must be quiet

So the comma helps separate the two parts, just as in English.

This sentence is natural and correct.

A native speaker might also say similar things such as:

• כשהמורה מדברת, שותקים.
• כשמורה מדברת, צריך לשתוק.
• כשמדברים עם המורה, לא מפריעים.

But כשהמורה מדברת, צריך לשתוק sounds completely normal, especially as a rule or instruction in a classroom.

You would change the verb to masculine singular:

• כשהמורה מדבר, צריך לשתוק.

Only מדברת changes to מדבר.

The noun המורה stays the same in ordinary unpointed spelling, which is one reason learners often rely on the verb to identify gender.