Each page has a number of test statements, each of which describes a given effect which should be seen. If the effects you see do not match the description given, then there is a problem with your browser's CSS support. The test statements on each page are duplicated inside a one-cell table. This was done to provide at least rudimentary testing of conformance within tables, which are know to be a weak point in many CSS implementations.
Above the test statements, the style declarations for that specific page are displayed. There are also navigation links at the top and bottom of the page. The top of the page will look something like this:
[Next] [Previous] [Section] [Contents] [Reference Image] [Specification]
The first line is not only the page's title, but also includes the name of the property being tested on that page, and its section number in the CSS1 specification. The six links under the title are, respectively:
Finally, it is assumed that visual user agents are being tested against this test suite, and the test statements are written with this assumption in mind. There are currently no provisions given for text-only agents, although these should still be testable, or for speaking browsers, which are beyond the scope of CSS1 in any case.
In the first place, you will need to make sure that you are not using a user-defined style sheet. If you have set up your own style sheet and have your browser configured to use it, then you will need to disable this feature before you start.
Furthermore, you will need to make sure that your browser is configured to pay attention to style sheets at all. This is typically done by finding an entry in your preferences dialog which says something like "Enable style sheets" and making sure the appropriate box is checked. You may have to enable other features as well. Please read the article Enabling Your Style Sheets if you don't know if style sheets are turned on in your browser, and don't know how to find out.
You will also want to be using a browser which is able to load LINKed style sheets. Every page in the suite uses the style sheet base.css. This provides a consistent look to the pages, and so when something overrides the base style sheet, you'll know it.