A leitura do medidor aparece na conta de luz.

Here leitura means reading in the sense of a measured value, not reading a book or text.

So a leitura do medidor means the meter reading.

This is a very common use in utility contexts:

• leitura do medidor = meter reading
• leitura da água = water meter reading
• leitura do gás = gas meter reading

Because do is the contraction of de + o.

• de = of
• o = the
• do = of the

So:

• a leitura do medidor = the reading of the meter

Portuguese uses these contractions very regularly, so de o would sound wrong in normal speech and writing.

Other common examples:

• da = de + a
• dos = de + os
• das = de + as

Because na is the contraction of em + a.

• em = in / on
• a = the
• na = in the / on the

So:

• aparece na conta de luz = appears on the electricity bill

As with do, this contraction is standard Portuguese.

Other related forms:

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

This is just the normal everyday Brazilian way to say it.

Literally, conta de luz is something like light bill, but in real usage it means electricity bill.

A few useful notes:

• conta de luz = everyday, very common
• conta de energia = also common
• fatura de energia elétrica = more formal or official

So even though the literal wording is different from English, the meaning is the same.

Yes, aparece literally means appears, but in this kind of sentence it often means:

• appears
• shows up
• is shown
• is listed

So A leitura do medidor aparece na conta de luz can be understood as:

• The meter reading appears on the electricity bill.
• The meter reading is shown on the electricity bill.

In practical English, is shown or is listed may sound more natural, but aparece is perfectly normal in Portuguese.

Because the subject is singular: A leitura do medidor.

The main noun is leitura, which is singular and feminine:

• A leitura = the reading

So the verb must also be singular:

• A leitura ... aparece

If the subject were plural, the verb would change:

• As leituras do medidor aparecem na conta de luz.
• The meter readings appear on the electricity bill.

Portuguese often uses definite articles more broadly than English does.

Here A leitura means the reading. In Portuguese, using the article sounds natural because it refers to a specific reading, the one connected with that meter and that bill.

English sometimes uses articles differently, so you cannot always translate word for word.

Compare:

• A leitura do medidor = the meter reading
• Leitura do medidor = meter reading / reading of the meter, more like a label, heading, or very general expression

In a full normal sentence, A leitura do medidor is the natural choice.

Yes, you could, and it would sound natural.

There is a slight difference in feel:

• aparece na conta de luz = appears / is shown on the bill
• está na conta de luz = is on the bill

So:

• aparece emphasizes visibility or presentation
• está simply states location or presence

Both are possible, but aparece fits especially well when talking about information displayed on a document.

In this sentence, yes, that is the natural interpretation because of conta de luz.

But medidor by itself is a general word meaning meter or measuring device. The exact type depends on context.

For example:

• medidor de luz = electricity meter
• medidor de água = water meter
• medidor de gás = gas meter

Since the sentence mentions the electricity bill, learners should understand medidor here as the electricity meter.

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

Normal version:

• A leitura do medidor aparece na conta de luz.

You could also hear:

• Na conta de luz, aparece a leitura do medidor.

That version puts more focus on na conta de luz.

Portuguese allows some flexibility in word order, but for a learner, the original sentence is the safest pattern:

• subject + verb + place/complement

Yes, it is natural and understandable in Brazilian Portuguese.

Depending on context, Brazilians might also say:

• A leitura do medidor vem na conta de luz.
• A leitura do medidor está na conta de luz.
• A conta de luz mostra a leitura do medidor.

These all express a similar idea, but the original sentence is completely normal.