To do a preview you have to go to the first sidebar-tab. Here, you find options for your entire project: Start a new project, open an existing project, export your current project, select the scene that starts off your project – and of course the preview.
Start a preview by simply clicking on the obvious “Start Preview” button. A new window will open on top of the VRdirect Studio that enables you to check your project by navigating through it. Before making any changes on your existing project, make sure to close the preview window again. Please make sure to save your project once in a while by clicking on “Save Project” in the tool bar at the top.