Yes, you are beginning to understand it, but I think you'll find downloading and reading Victoria's free
Quick Start Guide will answer many of your questions, and put you on a firm footing going forward.
Specifically answering your questions:
1. The strip at the bottom is called the Filmstrip. The Library module is the main module for organising images. In there are a lot of different tools to help you determine which is your best image out of a series, such as the Survey View and Compare View. Once you've decided which is the best you can use many methods to indicate it, such as applying a colour label, or a star rating, or a pick flag, or a keyword, etc.
2. No, Lightroom does not make backup copies of your files (other than the "Make Second Copy" option during import), if you are referring to the backup which can be run when you exit the program that it only backing up the catalog (the database which contains all the information about the imported images, which makes it vital to backup). Your image files need to be backed up by you separately. Lots of utilities available to help you do this.
Download Victoria's book and a lot of this will become clear.