Puella cancrum capit.

Because cancrum is the accusative singular form, which marks the direct object of the verb.

• cancer = the crab as the subject form (nominative singular)
• cancrum = the crab as the object form (accusative singular)

Since the girl is doing the action and the crab is receiving it, Latin uses cancrum.

You can tell from the noun endings.

• puella is in the nominative case, which usually marks the subject
• cancrum is in the accusative case, which usually marks the direct object

So puella is the one performing the action, and cancrum is the thing being caught.

Capit is from the verb capere, meaning to seize, take, catch, capture.

In this sentence, capit means she catches or she is catching.

Form details:

• capit = 3rd person singular
• so it means he/she/it catches

Because the subject is puella (girl), here it means she catches.

Because the verb ending already tells you the person and number.

In capit, the ending -it tells you:

• 3rd person
• singular

So Latin does not need a separate subject pronoun unless you want emphasis or contrast.

For example:

• capit = she/he/it catches
• ea capit = she catches with extra emphasis on she

Yes. Latin word order is much more flexible than English because the endings show each word’s job.

These can all mean the same basic thing:

• Puella cancrum capit
• Cancrum puella capit
• Capit puella cancrum

The most common neutral Latin order often puts the verb at the end, as in Puella cancrum capit.

Different orders can give different emphasis, but the case endings still tell you that:

• puella = subject
• cancrum = object

Puella is a first-declension noun.

Its basic forms are:

• puella = nominative singular
• puellae = genitive singular

In this sentence, puella is nominative singular, so it is the subject: the girl.

Cancer is a second-declension masculine noun.

Its key forms are:

• cancer = nominative singular
• cancri = genitive singular

Its accusative singular is cancrum.

This happens because second-declension masculine nouns normally take -um in the accusative singular. So when crab is the direct object, cancer changes to cancrum.

Actually, verbs ending in -ere are not first conjugation. First-conjugation verbs end in -are.

Capere is a third-conjugation verb.

Compare:

• amare = first conjugation
• monere = second conjugation
• capere = third conjugation
• audire = fourth conjugation

Its present tense forms include:

• capio = I catch
• capis = you catch
• capit = he/she/it catches

So capit fits the third-conjugation pattern.

It is a present tense form, but English can translate Latin present tense in more than one way depending on context.

So capit could be translated as:

• catches
• is catching
• sometimes even does catch for emphasis

Without more context, she catches the crab is the simplest translation.

A common classroom pronunciation would be roughly:

poo-EL-la KAHN-kroom KAH-pit

More specifically:

• puella ≈ poo-EL-la
• cancrum ≈ KAHN-kroom
• capit ≈ KAH-pit

A few helpful notes:

• c in Latin is always hard, like k
• ae is often pronounced like eye in restored classical pronunciation, though in many classrooms it may sound closer to eh in some contexts; here there is no ae
• stress in puella falls on the el
• stress in cancrum falls on the first syllable
• stress in capit falls on the first syllable

Yes. Latin has no articles like English the or a/an.

So puella cancrum capit could mean:

• the girl catches the crab
• the girl catches a crab
• a girl catches the crab
• a girl catches a crab

Which one is best depends on context. In beginner sentences, English often uses the by default, but Latin itself does not specify that here.

You would switch the cases:

• Cancer puellam capit.

Why?

• cancer = nominative singular, so now the crab is the subject
• puellam = accusative singular, so now the girl is the object

This is a good example of why Latin endings matter so much more than word order.

The dictionary forms are:

• puella, puellae = girl
• cancer, cancri = crab
• capio, capere, cepi, captum = catch / seize / take

For nouns, dictionaries usually give:

• nominative singular
• genitive singular

For verbs, dictionaries usually give several principal parts, which help you build different tenses and forms.