Food and Gold

This is probably an easy question, but I've been using all of my supplies and havnt had time to see. Can you have over the amount of supplies of your capacity?
EX: If I have a capacity of 20000 and someone gives me 15000 but I already have 8000 will that 3000 just disappear? And also the opposite if my upkeep is more than my production what will happen? Will I go into debt or just die?

If you go over your stockpile level then you keep all the resources but your food/gold from your farms and mines will not increase any further. If you lose all your resources they go down to zero but don't go any lower - I actually use this feature to my advantage by building a second city and storing my army there (accepting that my food will drop to zero) but allowing my main city to continue to grow. I simply transport over some food when I want to go on a raid. Hope this helps!