There are many different types of books aimed at different audiences. Textbooks tend to encompass a whole topic area fairly generally and are aimed at students. Textbooks are great for getting a background understanding of a topic.
Some books are written on more focused topics. Some may be aimed at an academic audience or experts and some at novices. Some are practical, some are for general interest. Some are aimed at practitioners and are intended to be a core handbook for daily working. They take longer to publish than articles and websites so the most up-to-the-minute information is often not available in books.
For some modules you may be required to purchase some or all of the texts from the ‘essential reading’ on your reading lists. You may find the following retailers useful:
Abebooks - Online bookshop especially useful for second hand and out of print books.
Amazon - Online bookshop, offering new and second hand copies often cheaper than RRP.
Blackwells - Search and buy online.
Waterstones - Search and buy online.