Imperativ

English has one bare form for every command: "Read!", "Sit down!", whoever you are talking to. Ukrainian has three: one for ти (one person you know well), one for ви (several people, or one person you address politely), and a "let's" form for ми. For an English speaker the main decision is which "you" you are speaking to.

The ти-form grows out of the present tense. Take the "they" form and drop its ending: чита́ють → чита́й, пи́шуть → пиши́, сидя́ть → сиди́. A handful of everyday verbs end in a consonant instead: сядь (sit down), стань (stand), будь (be). The most common "let's" in the language is Ході́мо! "Let's go!": Ході́мо на ка́ву до «Льві́вської копа́льні ка́ви»! In speech you will also hear дава́й(те) + verb: Дава́йте подиви́мося. "Let's have a look."

Politeness. The -те form plus будь ла́ска is the standard polite request: Сіда́йте, будь ла́ска. "Please, take a seat." Будь ла́ска is itself an imperative, roughly "be so kind", which is why it pairs so naturally with commands. Using the ти-form with a stranger, a shop assistant or an older person sounds rude in Ukrainian, even though English "Sit down, please" carries nothing of the kind.

Don't. A negative command is simply не + imperative, with no helper word like English "don't": Не хвилю́йся! "Don't worry!" Не хвилю́йся, на Вели́кдень усі́ бу́дуть удо́ма. Negative commands usually use the imperfective verb: Відчини́ вікно́! "Open the window!" but Не відчиня́й вікно́! "Don't open the window!"