In addition to the brief background in the above link, DDB has both a web portal and mobile app. The web portal does all the things indicated in the above link, including creating, storing, and editing character sheets. But, of course, you need internet access to make use of the web portal features.
The mobile app (as of this writing) only provides purchased content (plus, the "free" basic rules). So the web app is a great resource for reading/referencing/searching any of any of the digital books you've purchased when you don't have internet access (provided you've downloaded/updated the contact while you had internet access!). Unfortunately, it currently does not give you access to your character sheet(s). That is a feature they may add in the future. Also, the interface to review those books is a little different than when looking at the same digital content on the web portal. Some may find the app interface more preferable when merely reading through the books.