If you want to preview an HTML page in a help viewer or web browser, simply select an HTML file from the Source Files list or the Visual TOC Builder and then choose a viewer from the "Preview" toolbar menu. By default, the "Preview" menu includes UniHelp and Apple Help Viewer (Mac), but you can easily add additional viewers and web browsers (such as Safari, Internet Explorer, Firefox and others) to that list by selecting "Modify Viewer List" from the "Preview" menu. Please note that only normal applications are supported. Trying to add a viewer that is a command line console application will produce a shell error.
If you want to test the HTML code of the current page you have open in HelpLogic's Code Editor, you can preview it by choosing a viewer/browser from the Editor's "Preview" menu.