Пока ждёшь такси, можно перекусить в кафе.

Russian often uses 2nd person singular to mean a generic you (like English when you’re waiting for a taxi… meaning “anyone in that situation”). It’s informal in tone.
If you want it to be more neutral/formal, you can use:

• Пока ждёте такси, можно перекусить в кафе. (polite/plural you)
• Пока вы ждёте такси, можно перекусить в кафе. (explicit you)

Пока here is a subordinating conjunction meaning while / as long as / until. In this sentence it introduces a time clause: Пока ждёшь такси = while you’re waiting for a taxi.

Because the sentence starts with a subordinate clause (Пока ждёшь такси) followed by the main clause (можно перекусить в кафе). In Russian, an initial subordinate clause is normally separated by a comma.

In Russian, after time words like пока / когда / как только, the verb is often in the present tense even when the meaning is future. So Пока ждёшь такси… can refer to a future situation: “While you’re waiting (later), you can…”

Можно is an impersonal modal word meaning it’s possible / one can / it’s allowed. Russian often avoids stating the subject, so the “doer” is understood from context.
You can add a person with the dative if you want:

• Пока ждёшь такси, тебе можно перекусить в кафе. (it’s possible/okay for you)

Можно перекусить… sounds more like a general suggestion or option: “You could grab a bite…”
Ты можешь перекусить… is more direct and personal: “You can (are able to) grab a bite…” It can sound like you’re specifically telling that person what they can do.

After можно, Russian typically uses an infinitive: можно + infinitive.
Перекусить is perfective because it suggests a single, complete action: grab a bite (once) while waiting.
If you used the imperfective перекусывать, it would sound more habitual/repeated: “(you can) snack (regularly).”

Перекусить means to have a quick snack / grab a bite, usually something small and not a full meal.
Поесть is more general: to eat (a meal) and can imply something more substantial.

It is functioning as the direct object (accusative), but такси is an indeclinable noun (a loanword). Its form stays the same in all cases:

• ждать такси (accusative in meaning, unchanged in form)

In Russian, ждать usually takes a direct object with no preposition: ждать такси / ждать автобус / ждать друга.
You can also say ждать чего? (genitive) in some contexts, but ждать такси is very common and natural.

Common options:

• Polite you: Пока ждёте такси, можно перекусить в кафе.
• Explicit polite subject: Пока вы ждёте такси, можно перекусить в кафе.
• Slightly more formal wording: Пока вы ожидаете такси, можно перекусить в кафе. ( ожидать is more formal than ждать )