If you purchased the software at a "retail" location, the 25-character product-key was included with the packaging.
If you made an online purchase, the product-key was E-mailed to you -- check it, and check your 'JunkMail' folder.
If your computer came pre-installed with a "trial" version of the software, and the trial-period has ended (30 days? 60 days?) then you can purchase a license-key at any "big-box" (Best Buy, Walmart) store -- it's printed on a plastic card, the size of a credit-card, to allow you to install
the software onto 1 computer. Costs about $99.
Or, uninstall the software, and download FREE "office-productivity" software from:
http://www.OpenOffice.Org to do word-processing, spread-sheets, and presentations.
FREE.