When donors contribute, the next step would be to thank them for their contribution. In ISP, you'll be able to generate the list of donors and also mark them as Thanked so you don't send them multiple letters or emails.
When you arrive on the Thank Donors page, you'll see how many donors you have to thank based on the contributions received and input into ISP. You'll also have the ability to narrow down the list with the specific Budget Category tied to the contribution and also based on a minimum amount.
When ready, click the Generate List | Mark As Thanked button at the bottom of the screen. This will generate a .CSV file with all the contact info you'll need to create letters.
On this Thank Donors screen, you also have the ability to view previously thanked donors. At the bottom, click the Previously Thanked button and a menu will appear listing the date and amount of donors that were thanked that day. Just click on one to generate another .CSV with that date's previously thanked information.