Where did I go wrong?

This is sad:


I haven't previously considered myself someone who can't keep a plant alive, but such appears to be the case. The bottom two plants, I admit, may owe their conditions to improper or insufficient watering. I don't really know what I'm doing--I just put them in the pot and water them every couple days; maybe that's wrong. But the flowers on top, I just bought on Friday! And I trimmed their stems before putting them in water and everything (as learned in my Floral Design class at BYU). Shouldn't cut flowers last at least a week? I am disappointed.