Scroll your browser to see them. You also supply a Sample Text - type something in, paste from the clipboard, or retrieve a file. For complex expressions you may prefer to return here and adjust them directly in the 'Search Expression' and 'Replace Expression' fields. When you move forward again in the Wizard your new terms are automatically incorporated into other program fields. If you highlight a reg exp operator or some literal text in the Expression list, the effect is seen as blue text in the sample.
Red text shows the other aspects of the sample affected by the overall search expression.
Black text is the part not affected. The Replace Expression is also broken down into component parts. Context highlighting is available here also. The Expression Type pick list quickly inserts them by number. The last screen puts everything together to show you the sample text and what the result will be if you were to implement the terms in Search and Replace on a real file.