A Visual Prolog project represents an executable or DLL programmed in Visual Prolog. You can open a project in the IDE (Integrated Development Environment) and work on that project (i.e. executable/DLL).
The IDE will remember a list of the projects it has opened, so that you can easily reopen one of your projects. You can open several projects is each their IDE and work on them in parallel (should you want to).
When you have a project open in the IDE you can navigate to the source files that the target (i.e. executable/DLL) is built from, and you can edit them. In the IDE you can also build, execute and debug the target.
So your main interaction with the project will be through the IDE. The top-level information about the project is described in a project file (with extension vipprj). The IDE will maintain the project file, and you will not need to look into the file. But actually the project file is relatively easy to understand when you are familiar with the concepts of a project.
When you create a new project you give it a name and decide which directory that should contain the project. The project file and several other files will be created in this directory (and optionally sub-directories). You can choose among project templates for GUI programs, command line programs, etc.
After the project has been created it is automatically built (compiled, linked, etc). This will produce an initial version of your target. Since the project is just created the target is not really interesting at this point, but a side effect of building a project is that the compiler will gather a lot of browse information about the entities in the program.
The browse information enables the IDE to provide a lot of ways to navigate around in your code. In the project tree there will be a lot of nodes corresponding to the entities in your program (including what is included from PFC (Prolog Foundation Classes). And in the Go to menu you will find lots of navigation means mostof which are based on the browse information.
Browse information becomes inaccurate when you edit files, because editing changesd the positions where things are located. But upon a successful build of the project the browse information will again be accurate. Unsuccesful builds may however make some useful browse information disappear until the build is again successful. Therefore it is advisable to try to keep code as compilable as possible and build regularly.
The Hello World! video tutorial demonstrates the basic IDE features. The IDE in the video is version is an older one from Visual Prolog 7.3, so there are deviations from the current IDE, but the basics is the same and most of the details are also the same.
There is much more detailed information to find about the IDE in the tutorial Ide/Environment Overview.