Thank you!
The goal is to get the highest score possible with a limited number of draws (which you see on the top left corner), it should explain this at the beginning in a little tutorial, maybe it didn't trigger for you. The next step, the key to do this, is upgrading the shop level (refreshing the shop), so that you can get to cards (and also abilities) that are much more complex (as it says in the in-game tooltip of the shop refresh function) and that synergize with other cards and abilities to create strategies that can lead you to some crazy high scores (like the ones other players posted in the game page's comment). After upgrading the shop to higher levels, you get more powerful cards that open up the door to more strategies and synergies, for example these cards and abilities:
Another key point is also to "expand" the board other than only expanding your deck, by adding card slots, which ensure you'll produce more points for each turn, because cards stay on the ground for longer and thus help you craft longer equations which in turn lead to more points for your final score.
As for the sorting by "value", I'm not quite sure what you mean, these are the available sorting types for cards in your deck:
Maybe you meant "type", in this case cards are first sorted by their type (first +N cards, then ×N, then for example [dice] cards, then [coin] cards, ecc...), and then by descending value (if the type is the same), so in your case it would be "×3", "×4", "×6".
By the way, thank you for playing, I'm happy you enjoyed the game!