Projects are generic containers for your source code, Makefiles, and binaries. Before you can perform any work in the IDE, you must first create projects to store your work. One of the more common projects is a QNX C/C++ Project.
When you create a file within a project, the IDE also creates a record (local history) of every time you change that file and how you change it. All files must belong to a project; you can't open an arbitrary file in the filesystem because you must work on a known set of resources. For Windows, dragging and dropping files works as long as the destination is a project or folder. Once a file is in a project folder, double-click the file's entry to open it in the appropriate editor.
For Unix-type hosts (such as Linux), filenames are case-sensitive, but for Windows they're not. For this reason, don't use case alone to distinguish files and projects. For example, Hello.c and hello.c refer to the same file in Windows but they're two separate files for a Unix-type host.