Index -> Playing the Game -> The Game Screen -> The Hand Area
This area (4) is at the bottom of the game screen, right below the playmat. All the cards in your hand are displayed here.
If you want more information on a card in hand, you can hover your cursor over that card to get a tooltip on the card.
You can also double-click on any card in hand to make a magnified image of it appear. Click the magnified image to close it.