Please give more information about your problem.
Very few tablets are supported directly by ADE (Digital Editions).
You need to run ADE / Adobe ADEPT DRM compatible software on the tablet,
such as the Bluefire, Aldiko (not iPad) or Overdrive app.
Look in the tablet's app store.
You then need to register that software on the tablet, and copy books from the computer using an alternative path such as a file manager.
iPad likes to make file copies as inconvenient as possible (silly Apple),
so you need an indirect alternative path to do the copy, such as Dropbox, iTunes, or send yourslef an email with the .epub file embedded