A operadora mantém a rede móvel.

Because operadora is a feminine noun in Portuguese, so it takes the feminine article a.

• a operadora = the operator / the carrier
• o operador = the operator (masculine)

In this context, operadora usually means a telephone/mobile carrier company, not necessarily a female person.

Here it most naturally refers to a company, especially in Brazilian Portuguese telecom language.

Common meanings of operadora:

• operator (a female operator, depending on context)
• carrier/provider/company in telecom contexts

So in a sentence about rede móvel, Brazilian speakers will usually understand operadora as the mobile carrier / network operator.

Because mantém is the conjugated form of the verb manter.

• manter = infinitive, to maintain / to keep
• mantém = he/she/it keeps/maintains

In this sentence, the subject is A operadora, which is third person singular, so the correct form is:

• A operadora mantém ...

This verb is irregular and follows the pattern of ter:

• ter → tem
• manter → mantém

The accent mark is important here.

• mantém = singular: he/she/it maintains
• mantêm = plural: they maintain

So:

• A operadora mantém a rede móvel.
• As operadoras mantêm a rede móvel.

The accent also helps show the stressed syllable.

Because in Portuguese, adjectives usually come after the noun.

• rede móvel = mobile network
• carro novo = new car
• cidade grande = big city

Putting the adjective before the noun is possible in some cases, but it often sounds literary, unusual, or changes the emphasis. In normal everyday Portuguese, rede móvel is the standard order.

Yes. Here móvel is an adjective meaning mobile.

It describes rede:

• rede = network
• móvel = mobile

So rede móvel is a noun + adjective combination.

A useful detail: móvel can also be a noun in other contexts, where it means piece of furniture. But here it is clearly an adjective.

Portuguese uses definite articles more often than English.

So where English may say:

• The carrier maintains mobile network infrastructure or
• sometimes omit an article in certain styles,

Portuguese naturally says:

• A operadora mantém a rede móvel.

Both operadora and rede are being presented as specific, identifiable things, so the definite article a sounds normal.

Yes. This sentence follows the basic Subject + Verb + Object order:

• A operadora = subject
• mantém = verb
• a rede móvel = object

So structurally it is very similar to English:

• The carrier maintains the mobile network.

It would become:

• As operadoras mantêm as redes móveis.

Changes:

• a → as for feminine plural article
• operadora → operadoras
• mantém → mantêm
• rede → redes
• móvel → móveis

This is a good sentence for noticing agreement in Portuguese.

In Brazilian Portuguese, mantém is pronounced roughly like mahn-TENG, with the stress on the last syllable.

A few pronunciation notes:

• man- sounds nasal
• -tém is stressed
• the em ending is nasal in Brazilian Portuguese

You do not pronounce it like English maintain even though the meanings are related.

Yes, rede móvel is natural and correct, especially in technical or telecom-related contexts.

You may also hear related expressions such as:

• rede celular = cellular network
• telefonia móvel = mobile telephony
• operadora de celular = mobile carrier

But rede móvel is a standard and very natural phrase.