You can use Platformus in two ways: as the NuGet packages or the source code. The system documentation contains relevant articles that tell more about this.
This is the most convenient and flexible way to use Platformus. Create an empty web application on ASP.NET Core and add our system to it as the NuGet packages. This allows you to add your own code (and whole extensions) to the project, but at the same time you still can update the Platformus when the new versions are released.
You can use our system as a base for your own products. When the required changes are too large, you can adapt the source code of the Platformus to your needs. The downside of this approach is the high complexity of subsequent updates (because your copy of the source code will be different from the original one).