A tampa desta panela está na pia.

A is the feminine singular definite article, so it means the.

• A tampa = the lid
• Uma tampa = a lid

Here the speaker is talking about one specific lid, not just any lid.

Desta is a contraction of de + esta.

• esta panela = this pot
• de esta panela → desta panela = of this pot

So a tampa desta panela literally means the lid of this pot.

Also, desta agrees with panela, which is feminine singular. If the noun were masculine, you would use deste instead.

Traditionally:

• desta = of this
• dessa = of that / of the one you mentioned

In everyday Brazilian Portuguese, though, essa/dessa are often used where a textbook might teach esta/desta. So in natural speech, many Brazilians would also say A tampa dessa panela está na pia.

Using desta is correct and clear; it just sounds a bit more precise or slightly more formal in many contexts.

Because estar is normally used for location.

• A tampa está na pia = the lid is in the sink
• A tampa é de vidro = the lid is made of glass

So:

• ser describes identity, essence, material, classification, etc.
• estar describes location and many states/conditions

For where something is, estar is the normal choice.

Because they are different words with different stress:

• esta = this; stress on the first syllable: ES-ta
• está = is from estar; stress on the last syllable: es-TA

The accent mark in está shows the stressed syllable and helps distinguish it from esta.

Na is a contraction of em + a.

• em = in / on / at depending on context
• a = the feminine singular article the
• em + a → na

So na pia means in the sink.

If the noun were masculine, you would usually get no instead:

• no prato = in/on the plate

In this sentence, the grammar shows it:

• A tampa
• desta panela
• na pia

All of those forms are feminine singular.

It is true that many Portuguese nouns ending in -a are feminine, but that is only a pattern, not a guarantee. What really tells you the gender here is the article and the agreeing words around the noun.

Yes.

• a tampa da panela = the lid of the pot
• a tampa desta panela = the lid of this pot

The version with desta is more specific because it points to a particular pot: this one. If the context already makes it obvious which pot you mean, da panela is also perfectly natural.

Yes. This is a very normal structure:

• A tampa desta panela = subject
• está = verb
• na pia = location

So it follows the common pattern subject + verb + place.

You could change the order for emphasis, but that would sound more marked, for example:

• Na pia está a tampa desta panela

That is grammatical, but the original sentence is the most neutral and natural version.

Pia usually means sink or basin.

By itself, it does not have to be specifically a kitchen sink, but in this sentence, because of panela (pot), the most natural interpretation is the kitchen sink.

So the context is what makes it feel like the sink in the kitchen.

Yes. Tampa is a general word for lid, cover, or cap, depending on the object.

For example, it can be used for:

• a pot lid
• a bottle cap
• a container lid
• a cover on something

In A tampa desta panela, the word clearly means the lid of the pot because panela tells you what kind of object it belongs to.