The CreateD3DApp function that is called by the AppInit function in WinMain has created most of the underpinnings of a Direct3D application, but it hasn't finished yet. Before D3dmain.cpp calls the rendering loop, CreateD3DApp must complete a few more tasks.
After copying the current render states into the application's local D3DAppRenderState structure, CreateD3DApp calls the OverrideDefaults function. OverrideDefaults is another function that must be supported by all samples that use D3dmain.cpp. Sometimes an application will do very little in its OverrideDefaults function; for example, the Oct1.c sample simply replaces the default name with the string, "Octagon D3D Example".
Now CreateD3DApp calls the D3DAppSetRenderState function, which simply checks the status of the saved render states and either resets them (if no render states were provided in the call) or saves them before calling the D3DAppISetRenderState function, which is discussed in Setting the Immediate-Mode Render State.
As a final step before entering the rendering loop, CreateD3DApp calls the ReleaseView and InitView functions. These functions, like OverrideDefaults, are implemented by each sample application. ReleaseView simply releases any objects created in a previous call to the InitView function. (InitView, as you recall, is first called as part of the AfterDeviceCreated callback function.) This final call to InitView sets up the viewport again (in case there have been changes since the device was created) and re-creates the sample's execute buffers. For more information about InitView, see Initializing the Viewport.
This is the end not only of the CreateD3DApp function in D3dmain.cpp; it is also the end of the AppInit function. Now that the code has finished with the initialization part of the work, it can enter the rendering loop.