You’d want to break it down into it’s various parts, learn how to accomplish each of those parts, and then bring them together into one final product. At just a short 1min look at that game I would break it down into these general parts.
- UI (either Unity built-in UI, or some other plugin like NGUI). Familiarise yourself with how to use these tools to display UI, perhaps some simple tween animations, etc.
- Learn to use Drag/drop within your chosen UI (both have some built in support for dragging and dropping so that cuts out some of the complicated stuff for you).
- Data structures. Plan out your game data, how are you going to store information about the “cards” and the rules for what beats what.
You could break this problem down in all sorts of ways, this is just the way that comes to mind for me first, It may also not cover the entire feature list of that game, as stated I only took a quick look at the basic gameplay.
Hope this helps.