You will need to import your Contact Record information first. Then, you will need to import your donation information in a second import. To ensure that the donation records are connected with the corresponding donor, be sure to include a column in the Donation Records spreadsheet called Contact ID. A contact ID is a unique way of identifying which contact is which, and ensures the donation information is linked to exactly the correct Contact Record in Sumac.
Be sure to follow along with these how-to videos to help you learn how to import donations: http://sumac.com/videos-import-data/