usually the only time the Apply button is greyed out is after the tool has been used already. Perhaps you used it with the Radius set to zero? That would look like nothing happened. Either click New Transform and make sure the Radius is larger than zero when you press Apply – or try the interactive mode, with some (or all) of the points of the spline selected, select the Chamfer tool (the way the book describes) then click in the same window part that contains the spline and left-click-drag left to right to get a chamfer that way.
If you aren’t sure if you have points selected or what parts of the interface I’m talking about etc. download the help files from Maxon’s Downloads/Documentation page and install it (once you have the file go to the Help menu in C4D, select Manual Install and choose the Help file you downloaded (don’t unzip it, C4D will do that)) and check out the first few sections under the Cinema4D part – Usage, Views and Viewports etc. etc.