Some textbooks are regularly updated and each updated version is given an edition number. Quite often your lecturer will recommend a specific edition or the "most up to date" edition. To find this, search for the book on Library Search and then Refine your results to books and Sort by Date-Newest - the most recently published edition will be at or near the top of the list.
For example if you need to get the most recent edition of Kumar and Clark's "Clinical Medicine" search for it, limit to books and then sort by the newest date:
If you click on the title to display the full description you will be able to see the edition details:
