Breakdown of Пожалуйста, купи где-нибудь пять подушек.
пять
five
купить
to buy (perfective)
пожалуйста
please
где-нибудь
anywhere / somewhere (unspecified)
Questions & Answers about Пожалуйста, купи где-нибудь пять подушек.
Why is it подушек instead of just dropping the -а from подушка to make подушк?
Подушка (pillow) is a feminine noun ending in -а. After the number пять (five), we need the genitive plural. Normally, feminine nouns drop the -а to form a "zero ending". However, dropping the -а here leaves a hard-to-say consonant cluster: -шк. To make it pronounceable, Russian inserts a "fleeting vowel" (е or о) between the consonants. So, подушк becomes подушек.
Why do we use the genitive plural for pillows here?
In Russian, quantities of five and above (like пять) require the noun following them to be in the genitive plural case. If the number was 2, 3, or 4, you would use the genitive singular instead.
Why use где-нибудь (somewhere) instead of где-то?
Где-то means "somewhere" (a specific place, but the speaker doesn't know where it is). Где-нибудь means "anywhere at all" (it doesn't matter where). Since the speaker is asking the person to buy pillows at any store they can find, где-нибудь is the natural choice for requests and commands.
Купи is the perfective imperative for "buy". Why use perfective here instead of imperfective (покупай)?