Here you can see an example of cards in your hand. You can tell form your Player Status that you have 3 Flux and Level 2 Mountain Folk Domain. This allows you to play either of the un-greyed cards, the Axe Captain or the Craig Scout. The others either require too much flux or too high a domain level for you to use.
Discard Button: This allows you to discard a card in your hand. You wont draw a new card at the end of a round if you have 7 or more cards so this is useful if you want to get a new card. It is also useful to use if understand the autodraw feature.