Almost happy
Yeah the game gives a lot of intentionally cryptic item descriptions, there's a good wiki where you can find out what all the items/trinkets/etc actually does, though for some figuring all of that out by yourself is part of the fun. Black and Blue hearts can extend your health beyond your current limit but they don't give you another heart container, so when you lose them you can't heal back up with red hearts. Black hearts have the added effect that they damage all enemies in a room when you lose one. When you get a message that something has appeared in the basement or whatever it basically means that you've unlocked something that can now appear in the game, like new items and bosses for example, but they'll only appear randomly like everything else in the game. Some doors are only open if you have full health and some will only open if you have less than one red heart.
