Yes, the dictionary lists both 'booth' and 'kiosk' (also 'stand' and 'stall') as translations of кио́ск.
Yes, купи́ is imperative singular. (I.e. you use it with people you address with «ты», for friends, younger children, and sometimes for people you perceive as peers).
There's also imperative plural form, купи́те. It's used for people you address with «вы» (i.e. for several people, or to show politeness when addressing one person.)
There are no waterproof rules but the general rule is "в" for "enclosed" spaces that have walls or clear borders and "на" for open spaces or events.
- this gives the rather counter-intuitive (in modern world) на вокзале and на почте. As a rule, major railway stations and post offices are buildings these days.
This raises an interesting question. Is this Russian sentence more likely to be about something like a freestanding newsstand — are tickets for something or other sold at such establishments in Russia? — or about the Russian equivalent of a stadium or concert venue box office? At the moment I'm having visions of the tent erected at the local Russian Orthodox church's cultural festival where they were selling meal tickets and the like, which may or may not have been labeled "киоск."
are tickets for something or other sold at such establishments in Russia?
I think lottery tickets (лотере́йные биле́ты) could be sold in freestanding newsstands.
Is there a rule that imperative sentences should end in an exclamation mark in English? I'm pretty sure we don't have such a rule in Russian (in fact, adding an exclamation mark will make this sentence look very impolite, as if you're shouting).
For me "close the door, please" - said without an exclamation mark - is an OK way to ask. Reinforcing the stereotype of the Brits being more polite, I guess :-) If I was asking for something more significant than just pushing the door closed behind you, I would probably go with something more like your polite construction.
Friend TriggerSmooth: I am neither fluent in Russian nor a linguist, but it is my understanding that the following is true. The “imperative” in Russian is one of four “moods”, and is used to give commands or advice. The other three moods are: Indicative; Conditional; and Subjunctive. A “tense” refers to the time of the action or state indicated by the verb. Therefore, the “imperative” is not a “tense.”