As for adding to the library, use the admin interface to create a new catalog root. You'll have to give it a name and a path to the local directory that holds your mp3s. Keep in mind that the name you give the catalog root will be used in URLs (i.e. /catalog/cover/[catalog root name]/[album dir]/... and /catalog/file/[catalog root name]/...mp3s...) In particular, remember that you'll have to set up an alias or DocumentRoot in apache for each catalog root under the virtual location /catalog/file. Or you can be clever and do what I did which was name my catalog roots the same name as my top-level directories (i.e. mp3-extreme, emusic) and just point apache to the parent directory of all your catalog roots. For instance:

My Music Directories:

/plato/audio/mp3-extreme
/plato/audio/emusic

My Catalog Roots:

mp3-extreme
/plato/audio/mp3-extreme

emusic
/plato/audio/emusic

My Apache Config:

Alias /catalog/file /plato/audio

Of course, I could have created just one catalog root for /plato/audio but I thought the collections were of different enough quality and origin that I wanted to keep them separate, at least under the covers (for instance, I can update them or rebuild them individually now).