This Squish IDE User's Guide explains all aspects and features of the squishide in detail. To learn how to use Squish, it is best to start with one of the Tutorials, and then at least skim read the User Guide and Tools Reference. This document is designed purely to provide details of the Squish IDE for those already familiar with Squish.
As noted in the tutorials, the Squish IDE works just like the Eclipse IDE. If you aren't used to Eclipse, it is crucial to understand the key concepts of Views and Perspectives. In Eclipse (and therefore in the Squish IDE), a View is essentially a child window (perhaps a dock window, or a tab in an existing window). A Perspective is a collection of Views arranged together. Both are accessible through the Window menu.
The Squish IDE is supplied with three Perspectives—Squish Test Management (which is the Perspective that the Squish IDE starts with), Squish Test Debugging, and Squish Spy. You can change these Perspectives to include additional Views (or to get rid of any Views that you don't want), and you can create your own Perspectives with exactly the Views you want. So if your windows change dramatically, it just means that the Perspective changed. You can always use the Window menu to change back to the Perspective you want.