Learn Hardcore Russian: Пожалуйста, дайте сдачу мелкими монетами. - Please give me the change in small coins.

пожАлуйста: stress on А
дАй(т)е: stress on А ; the т is often very soft/quick in speech
сдАчу: stress on the first А
мЕлкими: stress on Е
монЕтами: stress on Е

When пожалуйста is used as a parenthetical politeness word meaning please at the start of a sentence, it’s commonly set off by a comma: Пожалуйста, ....
If it’s integrated more tightly into the sentence, the comma may be omitted in informal writing, but Пожалуйста, дайте... is a very standard punctuation choice.

What form is дайте, and who am I addressing?

Дайте is the imperative of дать (to give) in the 2nd person plural. It can mean:

you (plural) give... (talking to multiple people), or
you (formal) give... (polite you to one person, e.g., a cashier)

So this sentence sounds politely directed to a service worker.

Why is the verb дать (perfective) used instead of давать (imperfective)?

In requests for a single completed action (a one-time result), Russian typically uses the perfective: дайте (give [once]/hand over).
Давайте (imperfective imperative) often sounds like let’s... or a more process-oriented/ongoing suggestion, and is less natural here for “hand me the change.”

What case is сдачу, and why?