The menu can be found at the top-right of the screen in game, to the right of the number of cards in deck and teh numberof completed decks; to the left of the game's story(?) book, your cheevos and teh settings. The icon looks like a magnifying glass and a pile of cards. See image above.

The cards highlighted(white) are the ones you've unlocked. Click them to see their effects and enable/disable gilding.
The non-highlighted(grey) cards are not yet unlocked. Click them to see their criteria for being unlocked. You can't see the effects of those, unfortunately.
The number in the gold square on each card indicates its gold level, that is how many levels of that card you bring with you every time you prestige (unless you disable it. )
If you didn't gild all cards you could when starting the present prestige, you can do this by clicking the "Gild" button in the bottom centre of the cards window.