Learn Hardcore Ukrainian: Петро залишив квітку на столі.

Петро is the subject of the sentence. In Ukrainian, although the flexible case system allows for various word orders, placing the subject first is common for clarity and emphasis.

Why does the noun квітка change to квітку in this sentence?

Квітку is in the accusative singular form. Feminine nouns ending in -а typically change their ending to -у when they serve as the direct object, which is why квітка becomes квітку here.

What does the verb залишив mean, and what can you say about its tense and aspect?

Залишив is the past tense, perfective form of the verb залишити, meaning left or left behind. The perfective aspect indicates that the action was completed.

How is the prepositional phrase на столі constructed, and what case is стіл in within this phrase?

На столі translates to "on the table." The preposition на indicates location, and стіл is put into the locative (or prepositional) case, which changes its ending to -і (forming столі) to denote where the action took place.