La kafo kostas unu eŭron.

La is the definite article, like English the. It shows that the speaker means a specific coffee, or the coffee already understood from the situation.

Unlike English, Esperanto has just one definite article: la. It does not change for gender, number, or case.

The ending -o marks a noun in Esperanto. So kafo is a noun meaning coffee.

This is one of the most useful patterns in Esperanto: if you see -o, you should usually think noun.

The base form is kosti, meaning to cost. The ending -as marks the present tense, so kostas means costs or is costing.

A helpful thing for English speakers: Esperanto verbs do not change according to the subject. So mi kostas, vi kostas, ĝi kostas, ili kostas all use kostas.

The -n shows the accusative, which usually marks the direct object. With kosti, the amount paid is treated as the direct object, so unu eŭron gets -n.

So in this sentence, la kafo is the thing doing the costing, and unu eŭron is the amount it costs.

Esperanto does not have an indefinite article like English a/an. When English says a euro in a price, it usually really means one euro, so Esperanto uses unu.

So unu eŭron is the natural way to say one euro.

In ordinary number phrases, the noun takes the accusative ending, while the numeral usually stays unchanged. That is why you get unu eŭron, not normally unun eŭron.

You can compare:

• unu eŭron
• du eŭrojn
• tri librojn

The important thing is that the noun shows the grammar clearly.

The letter ŭ is a short glide, roughly like an English w sound. In eŭ, you say something like ehw as one smooth unit.

Also, Esperanto stress is always on the second-to-last syllable. So:

• KA-fo
• KOS-tas
• U-nu
• EŬ-ron

A rough pronunciation of the whole sentence is: la KA-fo KOS-tas U-nu EŬ-ron

Not naturally. Esti means to be, so La kafo estas unu eŭro would sound like The coffee is one euro, as if the coffee and the coin were somehow the same thing.

To talk about price, Esperanto normally uses kosti. So La kafo kostas unu eŭron is the correct and natural way to say it.

The most neutral order is subject + verb + object, so La kafo kostas unu eŭron is the normal beginner-friendly version.

Esperanto word order is fairly flexible because the -n marks the object. So something like Unu eŭron kostas la kafo is grammatically possible, but it sounds more emphatic or stylistically marked. For everyday use, the original order is best.