Puella papilionem diu spectat, sed eum capere non vult.

Because puella is in the nominative singular, the case normally used for the subject.

• puella = girl
• nominative singular ending: -a

So puella spectat means the girl watches.

Because papilionem is in the accusative singular, the case used for the direct object.

The verb spectat means she watches / is watching, so we ask: watches what?
Answer: the butterfly.

The noun is:

• nominative: papilio = butterfly
• accusative: papilionem = butterfly as the object

So puella papilionem spectat literally means the girl watches the butterfly.

Diu is an adverb meaning for a long time or for a while.

It modifies the verb spectat:

• spectat = she watches
• diu spectat = she watches for a long time

A native English speaker may expect a preposition like for, but Latin often expresses this idea with a single adverb: diu.

Eum means him or it, and here it refers back to papilionem.

A butterfly in English is it, but Latin uses grammatical gender, and papilio is masculine. Because of that, the pronoun is masculine too:

• papilio = masculine noun
• eum = masculine accusative singular pronoun

So eum means him/it, referring to the butterfly.

Because Latin pronouns usually agree with the grammatical gender of the noun, not the real-life sex.

So even though a butterfly is not necessarily male:

• papilio is grammatically masculine
• therefore the pronoun is eum

This is very common in Latin and in many other languages. English does this much less often.

Because after vult (wants), Latin normally uses an infinitive.

• vult = she wants
• capere = to catch

So:

• capere vult = she wants to catch
• capere non vult = she does not want to catch

This is very similar to English want + to + verb.

Because non negates the verb phrase vult capere.

• vult = she wants
• non vult = she does not want

So eum capere non vult means she does not want to catch it.

Latin word order is flexible, so you may also see non eum capere vult or eum non capere vult in some contexts, but eum capere non vult is perfectly normal.

Because the Latin infinitive already includes the idea of to.

• capere = to catch
• not just catch

So Latin does not need a separate word corresponding to English to here.

Spectat is:

• third person singular
• present tense
• active voice
• from spectare = to watch/look at

So spectat means she watches, he watches, or it watches.
Here, because the subject is puella, it means she watches.

Vult is the third person singular present of velle, which means to want.

Its basic forms are irregular, so learners often need to memorize them separately. Here:

• vult = she wants
• non vult = she does not want

With the infinitive capere, it becomes she does not want to catch.

Latin relies much more on case endings than on word order.

In English, word order tells us who is doing what:

• The girl watches the butterfly is different from
• The butterfly watches the girl

In Latin, the endings already show the roles:

• puella = subject
• papilionem = object

So Latin can place words more freely. The sentence could be rearranged in several ways and still mean basically the same thing, though the emphasis might change.

Sed means but.

It connects the two parts of the sentence:

1. Puella papilionem diu spectat = The girl watches the butterfly for a long time
2. sed eum capere non vult = but she does not want to catch it

So sed marks a contrast between watching and not wanting to catch.

Yes, it often could.

Latin sometimes omits an object pronoun when the meaning is clear from context. So something like sed capere non vult could mean but she does not want to catch it/him, if the butterfly is already understood.

However, including eum makes the object explicit and can help clarity or emphasis.

Either can work, depending on context.

Latin present tense often covers both:

• she watches
• she is watching

So Puella papilionem diu spectat could be understood as:

• The girl watches the butterfly for a long time
• The girl is watching the butterfly for a long time

English chooses between simple and progressive more strictly than Latin does.

A common classroom pronunciation would be roughly:

PWEL-la pa-pi-lee-OH-nem DEE-oo SPEK-tat, sed EH-um ka-PEH-reh non wult

A few helpful points:

• pu in puella sounds like pw
• c in capere is always hard, like k
• v in restored classical pronunciation sounds like w
• diu is two vowel sounds together, roughly dee-oo

Pronunciation systems vary a little, but those basics will help a lot.