As ervilhas devem estar no congelador, atrás do peixe.

In Portuguese, definite articles are used much more often than in English. So as ervilhas literally means the peas, even if English might simply say peas in the same situation.

Here:

• as = the for a feminine plural noun
• ervilhas = peas

So as ervilhas is the natural way to say it.

You can tell from both the article and the noun ending:

• as = feminine plural the
• ervilhas ends in -s, so it is plural

The singular is:

• a ervilha = the pea

So:

• a ervilha = one pea
• as ervilhas = the peas

Devem estar is the 3rd person plural of dever + estar.

• devem = they should / they must / they are probably
• estar = to be

Together, devem estar can mean different things depending on context:

1. obligation / expectation
   They should be
2. probability / assumption
   They are probably

In this sentence, it often sounds like someone is saying where the peas are expected to be: They should be in the freezer.

Because estão would mean they are, as a plain statement of fact.

Compare:

• As ervilhas estão no congelador.
  = The peas are in the freezer.
• As ervilhas devem estar no congelador.
  = The peas should be / are probably in the freezer.

So devem estar adds uncertainty, expectation, or deduction.

Portuguese has two verbs for to be: ser and estar.

Here we use estar because the location of something is considered a temporary state or position.

• estar = location, temporary condition, current state
• ser = identity, permanent characteristics, definitions

So:

• As ervilhas estão no congelador. = correct
• As ervilhas são no congelador. = incorrect

No is a contraction of:

• em = in
• o = the (masculine singular)

So:

• em + o = no

That means:

• no congelador = in the freezer

Other common contractions are:

• na = em + a
• nos = em + os
• nas = em + as

Because congelador is a masculine singular noun.

So it takes:

• o congelador = the freezer
• no congelador = in the freezer

If the noun were feminine, you would use na instead.

Congelador means freezer.

In Portugal, this is the normal word for the freezer compartment or a freezer unit. So no congelador is a very natural way to say in the freezer.

Because atrás de means behind or at the back of, and de contracts with the article o.

Step by step:

• atrás de = behind
• o peixe = the fish
• de + o = do

So:

• atrás do peixe = behind the fish

The fixed part is really atrás de.

You use atrás de before a noun or pronoun:

• atrás da porta = behind the door
• atrás do carro = behind the car
• atrás dele = behind him / it

So in this sentence, atrás do peixe follows that normal pattern.

It depends on the situation. Peixe here can refer to:

• one fish item in the freezer, or
• fish as a food item in a general sense

Portuguese often uses the singular in cases where English might also use a more general noun, depending on context.

If there were several separate fish and you wanted to be explicit, you could say:

• atrás dos peixes = behind the fish

But atrás do peixe is perfectly natural if the speaker is referring to one fish item or to the fish as a known thing.

The structure is:

• As ervilhas = subject
• devem estar = verb phrase
• no congelador = place
• atrás do peixe = more specific location

So literally it is:

• The peas should be in the freezer, behind the fish.

This word order is very normal in Portuguese.

The comma adds a small pause and makes atrás do peixe sound like extra location detail.

Without the comma:

• As ervilhas devem estar no congelador atrás do peixe.

With the comma:

• As ervilhas devem estar no congelador, atrás do peixe.

Both can be understandable, but the comma helps separate:

1. the main location: no congelador
2. the more precise detail: atrás do peixe

So it sounds a bit clearer.

Yes. Dever can sometimes be translated as must, should, or ought to, depending on context.

For example:

• As ervilhas devem estar no congelador.
  could mean The peas should be in the freezer or The peas must be in the freezer or even The peas are probably in the freezer.

The exact English choice depends on tone and situation. If someone is guessing where they are, are probably may fit best. If someone is saying where they are supposed to be, should be fits well.

In European Portuguese, unstressed vowels are often reduced, so the sentence may sound more compressed than its spelling suggests.

A rough learner-friendly approximation is:

• Ash ervílyash devẽsh shtar nu cong'lador, atrásh du peish'.

A few useful points:

• as before a vowel often sounds like ash
• estar often sounds closer to shtar
• no is usually a short nu
• peixe sounds roughly like peish

This is only an approximation, but it helps explain why spoken European Portuguese can sound faster and less clearly separated than the written form.

Yes. That is the better version if you are stating it as a fact.

Compare:

• As ervilhas devem estar no congelador, atrás do peixe.
  = The peas should be / are probably in the freezer, behind the fish.
• As ervilhas estão no congelador, atrás do peixe.
  = The peas are in the freezer, behind the fish.

So the choice depends on whether you are certain or only assuming.