Deixei os pratos no escorredor enquanto secava os copos.

Deixei is the 1st person singular of deixar in the pretérito perfeito (the simple past / preterite).

Here it means I left or I put/left in a completed action sense. The speaker is describing one finished action:

• Deixei os pratos no escorredor = I left the plates in the dish rack

So deixei presents that action as something completed in the past.

Secava is the imperfect tense of secar. It suggests an ongoing, in-progress, or background action in the past.

So in this sentence:

• Deixei os pratos no escorredor = completed action
• enquanto secava os copos = action that was ongoing at the time

This is a very common pattern in Portuguese:

• pretérito perfeito for the main completed event
• imperfeito for the background action happening at the same time

If you said enquanto sequei os copos, it would sound wrong in standard usage here, because enquanto usually pairs naturally with an ongoing action when you mean while I was drying the glasses.

Because Portuguese often omits the subject pronoun when the verb ending already makes the subject clear.

• Deixei already tells us the subject is I
• So eu is unnecessary unless you want emphasis or contrast

Compare:

• Deixei os pratos no escorredor... = normal, natural
• Eu deixei os pratos no escorredor... = more emphatic, like I left the plates...

This is very common in Portuguese.

Here deixar means something like to leave, to put, or to leave something somewhere.

In this sentence:

• Deixei os pratos no escorredor = I left the plates in/on the dish rack

It does not mean leave in the sense of go away from a place. It means placing something somewhere and leaving it there.

Other examples:

• Deixei as chaves na mesa. = I left the keys on the table.
• Deixei o casaco no carro. = I left my coat in the car.

No is a contraction of:

• em
  • o = no

So:

• no escorredor = in the / on the dish rack

Portuguese very often contracts em with the definite article:

• em + o = no
• em + a = na
• em + os = nos
• em + as = nas

Examples:

• na cozinha = in the kitchen
• nos copos = in the glasses
• nas caixas = in the boxes

Portuguese uses definite articles much more often than English does.

So os pratos and os copos are perfectly natural, even where English would often just say:

• the plates
• the glasses

or sometimes even omit the article in translation depending on context.

In Portuguese, using the article here sounds normal because the speaker has specific plates and glasses in mind.

Escorredor usually means a dish rack, draining rack, or dish drainer.

In this sentence, o escorredor is the place where washed dishes are left to drain and dry.

In a kitchen context, a learner should understand:

• os pratos no escorredor = the plates in/on the dish rack

Depending on the object and region, English might translate it as dish rack, drainer, or drying rack.

For the same reason as with deixei: the subject I is understood from the verb.

• secava can mean I was drying, he/she was drying, or you were drying depending on context
• But here the context strongly suggests the same speaker is doing both actions

So enquanto secava os copos naturally means:

• while I was drying the glasses

You could say enquanto eu secava os copos, but it is less neutral and usually adds emphasis.

Usually, yes, but it can also correspond to whilst or as depending on style and context.

In this sentence:

• enquanto secava os copos = while I was drying the glasses

Its main job is to connect two actions happening at the same time.

Not usually in the same clear, completed sense as English I dried.

Secava is the imperfect, so it typically means:

• I was drying
• I used to dry
• I would dry (in a habitual past sense)

In this sentence, the best interpretation is:

• while I was drying the glasses

If you want the completed action I dried the glasses, Portuguese would normally use the preterite:

• sequei os copos

The sentence follows a very common and natural Portuguese order:

1. verb
2. direct object
3. place
4. time/simultaneous action clause

So:

• Deixei = verb
• os pratos = direct object
• no escorredor = location
• enquanto secava os copos = simultaneous background action

This order is straightforward and idiomatic. Portuguese word order is often flexible, but this version sounds very normal.

Usually copos means glasses rather than cups.

So:

• copo = drinking glass / tumbler
• chávena = cup (especially in European Portuguese)

In this sentence, secava os copos would normally be understood as I was drying the glasses.

Yes, but it changes the meaning.

• Deixei = one completed event in the past
• Deixava = habitual, repeated, or descriptive past action

So:

• Deixei os pratos no escorredor enquanto secava os copos.
  = I left the plates in the dish rack while I was drying the glasses.
  (one specific occasion)

• Deixava os pratos no escorredor enquanto secava os copos.
  = I used to leave the plates in the dish rack while I was drying the glasses.
  or
  = I would leave the plates in the dish rack while drying the glasses.
  (habit or repeated action)

So both are grammatical, but they do not mean the same thing.

A natural English translation could be:

• I left the plates in the dish rack while I was drying the glasses.

Depending on context, you might also say:

• I put the plates in the dish rack while I was drying the glasses.

That is because deixar here can sound a bit like leave or put and leave there.

Yes, a couple of things feel very natural in European Portuguese:

• escorredor is a very normal word for a dish rack/drainer
• copos would naturally be understood as glasses
• the omission of eu is very typical and natural

The grammar itself is not exclusive to Portugal, but the vocabulary and phrasing fit European Portuguese very well.