For newcomers to Lightroom, and even for those who may have been using Lightroom for a while, the concept of the catalog, together with your library of photos, can be an intimidating and confusing affair:
I’ve recently completed a full Lightroom 5 Essentials training class over at Wiley’s Digital Classroom, and the great folks there have been kind enough to make some of the videos available for free… including my Introduction to the Lightroom Catalog. Take a look and see; if you’ve struggled with Lightroom’s organization, I think this will help clear things up.