And to get the category items, you want to change the description in the short version and long version. You'll start here in your catalog categories and hit detailed edit on any of the items you want to work on:
Then, your short description will show up first in basics:
The long descriptions you will click the Items and Pages that show up on the catalog inside cart page where you then want to click on the item with a detailed message that you want:
Then you can update the long description. This should be more in depth and be a strong describer:
At that point, your descriptions for your item will now be complete. Advice on this is to keep the top (short description) as more of unique sentence or two about the item. Something like "Every dollar counts towards supporting the __________ (type of program, event etc...) and will be put towards _____________ (enter the donation program).