Treasure card making is a learning experience and requires some patience. When making treasure cards you have to be in battle, so pick a boss that is easy like the ones on Unicorn Way.
You make treasure cards during your card choosing turn.
1) Buy "tough" cards and "keen eyes" cards from the library
2) Fill up your treasure card side board with the toughs and keen eyes
3) Set up your deck with your attack cards and ones you want to make into treasures (basically any cards that aren't already 100% cards)
4) Start a battle with a weak enemy
5) When its your turn to pick cards, right click and discard a couple cards so you have room in your hand to draw a couple tough/keen eyes from your treasure card sideboard
6) Hurry and apply the toughs and keen eyes to the cards you want to be more accurate or stronger
7) Right-Click on the card you just made to send it back to your sideboard
8) Wait for your next turn. When you can no longer draw treasure cards you have to be finished for that round. Either kill your enemy or flee and start over.
Last but not least
When you're done a round of card making, open your deck, click on the treasure cards you made to send them out of your sideboard into your treasure card deck. Then you're ready to trade or use them for yourself :)