How you copy your file to your ebook reader will vary depending on which device you own.
Instructions for transferring a downloaded ebook to a Kindle are on Amazon’s website
at the following page: Kindle Personal Documents Service
Instructions for transferring a downloaded ebook to a Kobo are available on kobo.com
at the following page: Adding books to your Kobo eReader
For other models of ebook reader we recommend you look for help on the manufacturers website.