A most-basic iTunes question

I have a Mac Mini with my music on an external drive. After reading about improvements in sound after doing a clean install of Snow Leopard, I decided to go ahead and give it a try. Trouble is, I can't recall how to tell iTunes, which is now pristine, that the tunes on my external drive are the ones I want in my llibrary.
I know it's really simple, but ...
Thanks for helping me past this brain-block.
-- Howard
Make sure your external HD is mounted.

Start iTunes with the Option key held down. (That's the one with the symbol that looks like a shopping cart without wheels, also called "alt" on some keyboards.)

You'll get a dialog asking you to choose a library.
If you did a clean install your libraries are gone so the above won't work. You don't have a library to choose.

From your desktop, drag the external HD icon onto the iTunes icon in your dock. It will import everything on the HD into your library.
This useful guide might be interesting,

It explains step by step what you have to do.