"Gdzie jest reszta?"

Translation: Where is the rest?

[Jupy015]

I don't understand the difference between reszta and odpoczynek

[Jellei]

"odpoczynek" - when you sit in your armchair and rest.

"reszta" - the "change" you get in the shop, as well as the "rest" ("remainder"), for example "OK, Steve and Alex are here already... where's the rest?" or similar.