If you don't need DRM books, don't use ADE at all, but use the free Calibre instead. Saves lots of headaches.
To use ADE, you need to install the Sony Reader software first, even if you don't use it.
That installation also installs a driver that allows ADE to 'see' the Sony.
Then plug the Sony in to usb and run ADE, the Sony should show up in the left pane under devices.
Make sure your copy of ADE is authorized with your Adobe ID, and then Authorize Device to transfer the authorization to the Sony.
If you want to use library books, you probably need to install the old ADE (see below).
The new one has issues with Sony ereaders and library books.
There are lots of bugs in ADE2.0 (and 2.0.1). Try replacing ADE2.0 with the older but more reliable v1.7.2.
(You can have them both installed at once if you like.)
Version 1.7.2, it is a little difficult to find, available on Adobe site for Windows and for Mac.
The forum software is sometimes corrupting the link above. There shouldn't be a blank in 'editio ns.html'. The following redirects to the same page: http://tinyurl.com/diged172
Some people have found ADE trying to upgrade automatically.
It appears (not 100% sure) that if you install ADE2.0 as a new install (not as an upgrade) that your 1.7.2 will continue to run.
Probably best to say no if 2.0.x installation asks if you want to migrate your library.