The Well is used in the Invasion module. It's listed there on page 6.
Ah, so it does. In the "Additional Components" graphic on that very page it isn't listed which is what I was going by. Down below under Setup it mentions the Well. Thanks!
As for the reference card, it appears that the positive and negative values for each component are two sides of the same information, one being how many pieces to use, while the negative is how many to remove (netting you the positive number). I was trying to subtract the negative number from the positive to get a sum of some kind and it wasn't making sense.
Thanks for the replies!