It'll turn an average image into a good image by compensating for the errors made whilst using the camera. Crop out stray branches/people, excess sky (whatever), adjust WB by using the pointer or the drop down menu to the setting you should have set in the camera but forgot, ditto with getting the correct exposure/brightness/contrast. The new adjustment brush and gradient filter tools in Lightroom 2 are superb for recapturing blown skies etc. That's just the basics - sharpening and the complicated stuff for adjusting colour saturation etc all assist in enhancing your image.
In short it does electronically what the oldies used to do in the dark room to bring out the best in the exposure. It does all this without affecting the original image. It works best in RAW, rather less good, but still good enough with jpegs - are you shooting in RAW?
As to using it - I can't really help other than point you towards the video tutorials on Adobes web pages which should assist. I found it instinctive to use -(after a week or so) much more so than Photoshop. To me - if you want to be creative, opt for Photoshop, if you want to simply bring out the best of your photos, use Lightroorm.
It's also great for cataloguing and tagging your photographs and for saving backups remotely.