Learn Hardcore Esperanto: Mi kuras en koridoro.

The sentence means "I run in a corridor." It is structured with Mi as the subject (meaning "I"), kuras as the present tense verb (meaning "run"), and en koridoro as a prepositional phrase indicating location (meaning "in a corridor").

Why does the verb kuras end with -as?

In Esperanto, the ending -as marks the present tense. This ending is used uniformly regardless of the subject, so verbs do not change form based on who is doing the action.

Why is there no article before koridoro?

Esperanto does not have an indefinite article equivalent to the English "a". The definite article "la" is only used when referring to something specific. Here, koridoro is intended in a general or indefinite sense, so no article is needed.

What role does the preposition en play in this sentence, and why isn’t the noun modified further?

The word en means "in" and introduces a locational phrase. Because en already indicates where the action occurs, and the sentence is describing a static location, there is no need for the accusative ending (such as -n) on koridoro.

How can I tell that koridoro is a noun?

In Esperanto, all nouns end with -o. The ending in koridoro clearly shows that it is a noun.

What would change if I wanted to express movement into the corridor rather than just being within it?

If you wish to indicate a destination or direction (for example, "I run into the corridor"), you would typically add the accusative ending -n to koridoro, forming koridoron. This use of -n marks the noun as the target of movement rather than simply a location.