This is a screen shot of mine:
I have several hard drives linked to LR that are automatically 'active' when they're turned on and plugged in - you can see the 2009-2010 and 1TB back-up drives are greyed out so aren't plugged in. LR saves everything as a catalogue; this is a database of images, metadata and settings applied to images. It's a non-destructive programme but unlike ACR where you create a sidecar .XMP file for every adjustment to a raw, adjustments are just saved in this catalogue database and applied over the top of the image in a sense.
The whole catalogue of images (i.e. everything that you've loaded into LR) can be scrolled through, even when the drives containing the originals aren't plugged in, because the catalogue creates thumbnails as reference. I keep my catalogue on my mac - if the catalogue was on an external drive then that would have to be plugged in.
Anyway; as you can see from the screenshot, I have several drives with several main folders inside that each hold several sub-folders.
This is my working style and others may have more effective ways of working, but I create a folder on the hard drive - mine are geared around magazines I shoot for but for example, let's call this folder 'IMAGES'. What I then do is import a shoot - let's call this shoot 'PAT'S PORTRAITS' and put them in a folder of that name. That folder is then placed inside the 'IMAGES' folder. I go to the IMPORT button in LR, find the 'IMAGES' folder and import that. What happens is it will create 'IMAGES' in the side menu AND it will also import that 'PAT'S PORTRAITS' folder and the images within that.
Now you have established a link to your images folder. These folders can all be renamed at will (alt+click on the folder name in LR).
Every shoot from now on is put into a named folder relevant to that job, and dragged manually into 'IMAGES' and then imported through LR and that list will start growing down the side. That's your image database and the archive.
Some people use the import dialogue that imports directly from the card but it creates folders that are date coded; I prefer to name folders after specific jobs or places, as it's easier to refer back to. Of course, images will be keyworded, so that's another way of searching for images, but this means that even when you're not in LR, you can go onto your drive and search for an image much quicker.
I've probably made it sound very complicated
I used Aperture for a bit but didn't get on with it; I moved to LR and it just fell into place very quickly. There's a website called thelightroomlab.com that carries good tutorials (plus there are loads if you google 'lightroom tutorials') and the Scott Kelby books are supposed to be good also.