This is a deckbuilder so they are the number of cards left in your deck (on the left) and the number of cards you have already "used" on the right ("used" because it includes cards you played and cards you discarded at the end of a "day" - "day" being the three cards (upper left for how many you have played on this day) you can play per turn).
Note that the cards currently in front of you (your hand) are not counted in either pile.
Once you finish using your whole deck (the number on the left is zero) the deck is shuffled and you reuse your deck (the number on the right reset to zero and the number on the left becomes the size of your deck). You will notice a pause in your cards being dealt if this happens part way through dealing your cards for a day.
Knowing how far you are through your deck is useful (and becomes more useful as you get more cards) because if, for example, you used your sword on the first day then it is very unlikely to be dealt to you on the second day but equally if it wasn't dealt to you on your first day it must be dealt on the second day. This makes card counting a useful advanced strategy to making beating the game easier and makes beating the game in less than two weeks easier.
I hope this helps ;)