There are lots of books on Linux. It's a good idea to get one that relates to your particular distribution. O'Reilly & Associates is a publisher that produces quite a few good books on Linux and related technologies. They also have a useful program called Safari Bookshelf that lets you pay a monthly fee to maintain an online bookshelf where you can read books online from O'Reilly and other publishers.

One last note, if you are reading this you are probably a new Linux user. There is an effort underway to try to study the usability of Linux from the new user point of view. The study is being run at the GrokDoc website which you can find at www.grokdoc.net. Help put your inexperience to good use and help improve Linux for everyone by participating.