Puella comam longam habet.

Because puella is the subject of the sentence: the girl is the one doing the action of having.

In Latin, the subject is usually put in the nominative case. For a first-declension noun like puella, the nominative singular ending is -a.

So:

• puella = nominative singular = the girl / a girl as subject
• puellam = accusative singular = the girl as direct object

Here the girl is not being acted on; she is the one who has something.

Because comam is the direct object of habet.

The direct object is the thing being had. In this sentence, the girl has hair, so comam is in the accusative case.

For a first-declension noun like coma, the accusative singular ending is -am.

So:

• coma = nominative singular
• comam = accusative singular

Latin marks the job of a noun in the sentence by its case ending, not mainly by word order as English does.

Because longam is an adjective describing comam, and Latin adjectives must agree with the nouns they describe in:

• gender
• number
• case

Since comam is:

• feminine
• singular
• accusative

the adjective must also be:

• feminine
• singular
• accusative

So we get longam, not longa or longus.

This agreement is one of the main ways Latin shows which words belong together.

We know because of agreement.

• puella is nominative singular feminine
• comam is accusative singular feminine
• longam is accusative singular feminine

Since longam matches comam in case, number, and gender, it goes with comam.

If the sentence meant the long girl has hair, then the adjective describing puella would need to be nominative too, for example puella longa.

So the form of the adjective tells you what it modifies.

Habet is the verb, from habere, meaning to have.

The ending -t tells you it is:

• third person
• singular
• present tense

So habet means he/she/it has.

Because the subject here is puella, we understand it as she has.

Latin often does not need an explicit subject pronoun, because the verb ending already tells you the person and number.

In habet, the ending -t already means he/she/it singular.

So Latin can simply say:

• Puella comam longam habet

and there is no need to add a separate word for she.

A pronoun such as ea might be added only if the speaker wants emphasis or contrast.

Classical Latin does not have articles like English a, an, and the.

So puella can mean:

• a girl
• the girl

and comam can mean:

• hair
• the hair
• sometimes more naturally a head of hair, depending on context

The context tells you which English article is best in translation.

Word order in Latin is more flexible than in English, because case endings already show the grammatical roles.

So all of these could express roughly the same basic idea:

• Puella comam longam habet
• Puella longam comam habet
• Comam longam puella habet

The endings tell you that:

• puella is the subject
• comam is the object
• longam describes comam

That said, word order is not meaningless. Different orders can sound more natural, emphatic, or stylistically marked. The version you have is a normal, straightforward sentence.

Latin coma is often used as a singular noun meaning hair in the sense of a mass of hair or head of hair.

English usually treats hair as a mass noun, so we do not normally say a hair when we mean all the hair on someone's head. Latin can use a singular noun more naturally here.

So comam longam means something like:

• long hair
• a long head of hair

depending on how naturally you want to express it in English.

Yes. Since Latin has no articles, puella by itself can mean either a girl or the girl.

The same is true for many Latin nouns. You decide from context which English translation fits best.

So in a sentence like this, the Latin does not force one choice:

• A girl has long hair
• The girl has long hair

Both are possible unless the wider context makes one of them clearer.