Eu deixei o pacote sobre a mesa, ao lado do envelope que veio pelo correio.

Yes, you often can leave it out.

Portuguese verbs usually show who the subject is, and deixei already tells us the subject is I. So both of these are natural:

• Eu deixei o pacote...
• Deixei o pacote...

Including Eu can add clarity, contrast, or emphasis. For example, Eu deixei o pacote, não ele = I left the package, not him.

Here, deixei means I left in the sense of I placed / I put and left there.

In Portuguese, deixar is very common and can mean several things depending on context, including:

• to leave something somewhere
• to let / allow
• to abandon
• to leave behind

In this sentence, it means something like I left the package on the table.

Deixei is the pretérito perfeito (simple past / preterite) of deixar.

It refers to a completed action in the past:

• Eu deixei = I left
• Você deixou = you left
• Ele deixou = he left

So the sentence describes a finished action: the speaker put the package there at some point in the past.

Portuguese uses definite articles very frequently, often more regularly than English.

So:

• o pacote = the package
• a mesa = the table
• o envelope = the envelope
• o correio = the mail / the postal service

In many contexts where English might be more flexible, Portuguese still prefers the article. This is very normal.

Yes. Sobre a mesa means on the table.

Here, sobre means on / on top of / over, depending on context. In this sentence, it means the package was placed on the table.

A learner should know that sobre can also mean about / regarding in other contexts:

• um livro sobre música = a book about music

So context matters.

It is correct and natural, but not the only possibility.

Another very common option is:

• em cima da mesa

That also means on the table.

There can be slight differences depending on context and style:

• sobre a mesa can sound a little more neutral or written
• em cima da mesa is very common in everyday speech

In this sentence, sobre a mesa is perfectly good Portuguese.

It means next to the envelope or beside the envelope.

Breakdown:

• ao lado de = next to / beside
• do envelope = of the envelope

So:

• ao lado do envelope = next to the envelope

This is a fixed expression in Portuguese and is very common.

Because Portuguese normally contracts certain prepositions with articles.

Here you have two contractions:

• a + o = ao
• de + o = do

So:

• a o lado de o envelope becomes ao lado do envelope

This is standard Portuguese grammar, not optional in normal usage.

Some other common contractions are:

• de + a = da
• em + o = no
• em + a = na
• por + o = pelo
• por + a = pela

It describes o envelope.

So the structure is:

• o envelope que veio pelo correio
• the envelope that came in the mail

The word que here is a relative pronoun meaning that / which.

So the full noun phrase is:

• do envelope que veio pelo correio
• of the envelope that came by mail

Because of position and structure.

In Portuguese, a relative clause introduced by que usually attaches to the closest logical noun before it. Here that noun is o envelope:

• ao lado do envelope que veio pelo correio

So the most natural reading is:

• the envelope that came by mail

If the speaker wanted that came by mail to describe the package, they would normally restructure the sentence to make that clearer.

Veio is the simple past of vir (to come) for ele/ela/você.

Here it matches o envelope, which is singular:

• o envelope veio = the envelope came

So:

• o envelope que veio pelo correio = the envelope that came by mail

If it were plural, it would be:

• os envelopes que vieram pelo correio = the envelopes that came by mail

Pelo correio means by mail, through the mail, or via the postal service.

It is made of:

• por + o = pelo
• correio = mail / post / postal service

So:

• veio pelo correio = came by mail

This is a very common expression.

Portuguese often uses the article with correio in this expression.

So the normal form is:

• pelo correio

Literally, it is through the mail / through the postal service.

The contraction is required:

• por + o correio = pelo correio

Usually yes, in this kind of sentence.

Correio can refer to:

• mail / post as a system
• the postal service
• sometimes the post office, depending on context

So veio pelo correio means the envelope arrived through the postal system, not by hand, for example.

The comma separates the main statement from extra location information.

Main idea:

• Eu deixei o pacote sobre a mesa

Added detail:

• ao lado do envelope que veio pelo correio

In many cases, Portuguese punctuation with phrases like this can be somewhat flexible. The sentence is fine with the comma, and it helps the reader process the added detail more clearly.

Without the comma, the sentence could still be understandable:

• Eu deixei o pacote sobre a mesa ao lado do envelope que veio pelo correio.

But the comma gives a slight pause and can make the structure easier to read.

Sometimes, but it changes the meaning a bit.

• sobre a mesa = on the table
• na mesa = literally in/on the table, but often understood as at the table or on the table, depending on context

If you want to be very clear that the package was resting on top of the table, sobre a mesa or em cima da mesa is better.

Yes, often.

• deixei o pacote sobre a mesa = I left the package on the table
• coloquei o pacote sobre a mesa = I put the package on the table

The difference is subtle:

• coloquei focuses more on the act of placing
• deixei often suggests both placing it there and leaving it there

In this sentence, deixei sounds very natural.

A simple breakdown is:

• Eu = subject
• deixei = verb
• o pacote = direct object
• sobre a mesa = location
• ao lado do envelope que veio pelo correio = more detail about location
• que veio pelo correio = relative clause describing o envelope

So the sentence is built like this:

I left + the package + on the table + next to the envelope + that came by mail