Learn Hardcore Esperanto: Mi kreas novan libron kun amikoj.

kreas comes from the root meaning "to create". The -as ending shows that the verb is in the present tense, so it means "I create" or "I am creating".

Why do both novan and libron have an -n ending, and how does the accusative case work in Esperanto?

In Esperanto, the -n ending marks the accusative case, which is used for the direct object of a verb. Here, libro (book) is the direct object, so it becomes libron. Since adjectives usually agree with the noun they modify, nova also takes the accusative ending, becoming novan, to indicate that it describes the direct object.

What does the phrase kun amikoj mean, and how is the preposition kun used in this sentence?

The phrase kun amikoj translates to "with friends". The preposition kun means "with" and connects the action of creating the book to the company of friends. Notice that the noun amikoj remains in its base form (nominative plural) because prepositional objects do not require an accusative ending unless indicating direction.

Is the word order in Esperanto similar to English, and how does the use of the -n ending affect sentence structure?

Esperanto typically follows a Subject-Verb-Object (SVO) word order, much like English. However, due to the consistent use of the -n ending to mark the direct object, Esperanto allows for fairly flexible word order without causing confusion. The -n ending makes it clear which noun is the object, even if the elements of the sentence are rearranged.