There's an few options.
- If you have a tablet or smartphone and you are connected to the Internet, clicking on the link to the .epub should automatically open it. You may need to install an epub reader app if you haven't already. There are many free ones to choose from. If your device is not connected to the internet, follow the manufacturers' instructions on transfering files.
- If you are using a desktop or laptop computer and don't need offline access, there are several free browser extensions for firefox and chrome that allow you to read the book within the browser.
- If you are using a desktop or laptop and need or prefer offline access, download the book to your computer and then use an ebook manager tool like Calibre to read the book.
- If you have a Kindle, you can use Calibre to transform the book into a PDF or .mobi format for viewing on your Kindle.