Eu guardo os pratos na prateleira de cima.

Yes, you often can omit eu in Portuguese because the verb form guardo already shows that the subject is I.

• Eu guardo os pratos... = I put away/store the dishes...
• Guardo os pratos... = same meaning in many contexts

Speakers include eu when they want to:

• add emphasis
• create contrast, like I put away the dishes, not someone else
• make the subject especially clear

So eu is correct, but not always necessary.

Guardo comes from the verb guardar. In this sentence, it means something like:

• I put away
• I keep
• I store

With os pratos, the most natural English idea is often I put the dishes away on the top shelf or I keep the dishes on the top shelf.

So guardar is broader than just one English verb. The exact translation depends on context.

Guardo is the present indicative form of guardar for eu.

It can mean:

• I put away
• I keep/store
• sometimes, depending on context, I usually keep

Conjugation in the present:

• eu guardo
• você/ele/ela guarda
• nós guardamos
• vocês/eles/elas guardam

Portuguese uses definite articles like o, a, os, as more often than English.

• os pratos = the dishes
• pratos = dishes

In Portuguese, it is very natural to say os pratos when referring to a specific set or to dishes in a general household sense. English often leaves the out in places where Portuguese keeps it.

So Eu guardo os pratos... sounds more natural than just Eu guardo pratos... in most everyday contexts.

Na is a contraction of:

• em
  • a = na

So:

• em a prateleira → na prateleira

Because prateleira is a feminine singular noun, it takes a, and with em it becomes na.

Examples:

• no armário = em + o
• na cozinha = em + a
• nos pratos = em + os
• nas caixas = em + as

Because in Portuguese, nouns have grammatical gender. Prateleira is a feminine noun, so it uses feminine articles and related forms:

• a prateleira
• na prateleira

This is grammatical gender, not biological gender. It is simply part of how the noun behaves in the language.

De cima literally means something like from above or of the top, but in this kind of phrase it means:

• upper
• top
• on top

So a prateleira de cima means:

• the top shelf
• the upper shelf

This is a very common Portuguese way to describe location by position:

• o andar de cima = the upstairs floor / the floor above
• a gaveta de baixo = the bottom drawer

Portuguese often prefers descriptive phrases where English may use a single adjective.

So:

• prateleira de cima = top shelf / shelf above
• prateleira de baixo = bottom shelf

You may also see more formal adjectives like superior, but in everyday speech de cima sounds very natural.

Yes. Even though em can sometimes translate as in, on, or at, the natural English translation here is on the shelf.

Portuguese em is broader than English prepositions. Its exact meaning depends on context.

So:

• na prateleira = on the shelf not usually in the shelf

It can mean either, depending on context.

Possible meanings:

• I keep the dishes on the top shelf → a usual arrangement or habit
• I put the dishes away on the top shelf → what I am doing / what I do

Portuguese present tense is flexible, just like English present can sometimes be.

If you want to stress an action happening right now, Brazilian Portuguese often uses:

• Estou guardando os pratos na prateleira de cima. = I am putting the dishes away on the top shelf.

Yes, but the original order is the most neutral and natural.

Standard order:

• Eu guardo os pratos na prateleira de cima.

You could also say:

• Os pratos eu guardo na prateleira de cima.

That version gives extra emphasis to os pratos, as if contrasting them with something else.

So the original sentence is the best default choice for a learner.

Because of the structure of the phrase:

• na prateleira de cima

Here, de cima comes directly after prateleira, so it naturally modifies prateleira.

The meaning is:

• in/on the shelf that is on top not
• the dishes from above

So the sentence is understood as:

• I keep/put away the dishes on the top shelf.

Not in this sentence if you mean the top shelf.

• prateleira de cima = top shelf
• em cima usually means on top or above, often as an adverbial phrase

Compare:

• Os pratos estão em cima da mesa. = The dishes are on top of the table.
• a prateleira de cima = the top shelf

So de cima is the correct choice when identifying which shelf.