שים את הצלחת על המגש, בבקשה.

שים is the masculine singular imperative form of the verb לשים (to put / to place).

So if you are speaking to one male, you say:

• שים את הצלחת על המגש. — Put the plate on the tray.

This is the direct command form in Hebrew.

A useful note: in everyday spoken Hebrew, people very often use the future form instead of the formal imperative, so you may also hear:

• תשים את הצלחת על המגש.

That is very common in conversation, even though שים is the standard imperative form.

The form of to put changes depending on who you are speaking to:

• שים — to one male
• שימי — to one female
• שימו — to more than one person

So:

• שימי את הצלחת על המגש, בבקשה. — to one woman
• שימו את הצלחת על המגש, בבקשה. — to several people

את is the Hebrew marker for a definite direct object.
It usually is not translated into English.

In this sentence:

• שים — put
• את הצלחת — the plate (the direct object)
• על המגש — on the tray

Hebrew uses את before a direct object when that object is definite, such as:

• with ה = the
• with a name
• with a possessive

So here, הצלחת means the plate, which is definite, so Hebrew uses את:

• שים את הצלחת...

If it were indefinite, you would usually leave out את:

• שים צלחת על מגש. — Put a plate on a tray.

The prefix ה־ means the.

So:

• צלחת — a plate
• הצלחת — the plate

and

• מגש — a tray
• המגש — the tray

In your sentence, both nouns are definite:

• את הצלחת — the plate
• על המגש — on the tray

English uses a separate word, the, while Hebrew usually attaches it to the beginning of the noun.

Because הצלחת is the direct object of the verb, but המגש is not.

Breakdown:

• שים — put
• את הצלחת — the thing being put
• על המגש — where it is being put

The phrase על המגש is a prepositional phrase (on the tray), and prepositions do not take the direct object marker את in this kind of sentence.

So:

• את הצלחת → yes, because it is the definite direct object
• על המגש → no, because it follows the preposition על

על means on, onto, or upon, depending on context.

In this sentence:

• על המגש = on the tray

It tells you the location or destination of the action.

Some quick comparisons:

• על הכיסא — on the chair
• על השולחן — on the table
• על המגש — on the tray

The sentence follows a very common Hebrew pattern:

verb + direct object + prepositional phrase + בבקשה

So here:

• שים — verb
• את הצלחת — direct object
• על המגש — prepositional phrase
• בבקשה — please

This is a very natural order in Hebrew for commands.

Here, בבקשה means please.

So:

• שים את הצלחת על המגש, בבקשה.

That is a polite command: Please put the plate on the tray.

In Hebrew, בבקשה is very flexible. It can appear:

• at the end: שים את הצלחת על המגש, בבקשה.
• at the beginning: בבקשה, שים את הצלחת על המגש.

Both are natural.

Also, בבקשה can mean other things in different contexts, such as you’re welcome or here you go, so its meaning depends on the situation.

A simple pronunciation guide is:

sim et ha-tsalakhat al ha-magash, bevakasha

A few notes:

• שים sounds like sim
• צלחת is roughly tsa-LA-khat
  
  • the ח is a throaty sound, often written kh
• מגש is roughly ma-GASH
• בבקשה is roughly be-va-ka-SHA

The stress is usually on:

• tsaLAkhat
• maGASH
• bevakaSHA

Yes, it is a little irregular-looking if you compare it to the infinitive לשים.

The verb is לשים (to put), but the imperative is:

• שים
• not something like לשום or a fully predictable form for beginners

So it is best to learn it as a common command form:

• שים — put! (to one male)
• שימי — put! (to one female)
• שימו — put! (to plural)

Because this is a very common verb, memorizing these forms early is useful.

Yes, sometimes צלחת can be translated as plate or dish, depending on context.

Most often, צלחת means plate, but in some situations English might use dish more naturally.

So the exact English choice depends on what kind of object is being discussed.

You could, but the meaning would change.

Your sentence means something like:

• Put the plate on the tray.

That sounds like both objects are specific and known.

If you want an indefinite meaning, you could say:

• שים צלחת על מגש.

That would mean:

• Put a plate on a tray.

Notice:

• no ה־
• no את

because צלחת is no longer definite.

It is basically neutral and polite.

• שים is a normal command form
• בבקשה makes it polite

So it works well in everyday situations.

However, in very casual spoken Hebrew, many speakers would say:

• תשים את הצלחת על המגש, בבקשה.

That sounds more conversational.
The version with שים is still completely correct and natural.