How can I use my gems and what are the impact of resting?

[larienna]

Gems seems to be usable to buy cards, I tried every button in every screen with left and right click and I could not find how I can buy cards with gems.

Is there a consequence in resting? Yes, you can reconfigure your deck and time advance, but is there a consequence of resting too much. Does something happens if too many days passes?

[Douzeju]

i don't think there is any drawback to resting, and you can buy cards at the campfire, there are 2 merchants there

[Knight Lamune]

Yeah I had already beat the game a couple plays through before I realized the camp screen actually had interactable characters in it.