A coleira é nova.

Because coleira is a feminine singular noun in Portuguese, so it takes the feminine singular definite article a.

Article agreement:

• o = masculine singular
• a = feminine singular
• os = masculine plural
• as = feminine plural

So:

• a coleira
• as coleiras

This is grammatical gender, not biological gender.

Here, a means the.

In Portuguese:

• a = the for a feminine singular noun
• uma = a/an for a feminine singular noun

So:

• A coleira é nova. = The collar is new.
• Uma coleira é nova. = A collar is new.

Because Portuguese nouns have grammatical gender, and coleira is simply classified as feminine.

A native English speaker often expects gender to match real-world sex, but in Portuguese that is usually not the point. Objects also have grammatical gender.

Many nouns ending in -a are feminine, and coleira follows that pattern. But remember: endings are helpful clues, not absolute rules.

É is the third-person singular present form of the verb ser, meaning is.

So:

• eu sou = I am
• você/ele/ela é = you/he/she is

The accent matters because:

• é = is
• e = and

So the accent helps distinguish two different words.

Because adjectives in Portuguese usually agree in gender and number with the noun they describe.

Since coleira is feminine singular, the adjective must also be feminine singular:

• coleira nova

Compare:

• o carro novo = the new car
• a coleira nova = the new collar
• os carros novos = the new cars
• as coleiras novas = the new collars

In Portuguese, adjectives often come after the noun, much more often than in English.

So:

• coleira nova literally looks like collar new

That is normal Portuguese word order.

In your sentence, though, the adjective is not directly after the noun because the sentence uses ser:

• A coleira é nova.

This structure is:

• subject: A coleira
• verb: é
• adjective: nova

So it works like The collar is new in English.

Yes, but the meaning changes slightly.

• A coleira é nova usually means the collar is new, as a basic fact.
• A coleira está nova usually means the collar is in a new-like condition, or looks new.

This is the common contrast between ser and estar:

• ser = identity, classification, more inherent description
• estar = state, condition, how something is at the moment

So if you are saying it is literally a new collar, é nova is the most direct choice.

Normally, no.

In standard Portuguese, a singular countable noun used as the subject usually needs an article or another determiner:

• A coleira é nova.
• Essa coleira é nova.
• Minha coleira é nova.

Coleira é nova sounds incomplete or unnatural in ordinary speech, except in very special styles such as headings, labels, or very reduced note-like language.

A common Brazilian pronunciation is approximately:

co-LAY-ra

More carefully:

• co sounds like co in code, but shorter
• lei sounds like lay
• the r in the middle is usually a quick tap
• the final a is often weak, closer to uh

A rough full-sentence pronunciation is:

a co-LAY-ra é NO-va

IPA, if helpful:

• A coleira é nova. = [a koˈlejɾɐ ɛ ˈnɔvɐ]

Very often, yes: coleira commonly refers to an animal collar, especially a dog collar.

Depending on context, it can also refer more generally to a collar-like strap or band worn around the neck.

So in many everyday situations, a learner will most naturally understand a coleira as the collar for a pet.