The docs say a lot:
Prototype of Shellexecute.
HINSTANCE ShellExecute(HWND hwnd,
First argument - handle to your window. If you don't have any, pass NULL.
Operation: passing "open" will open a document, file or whatever you specify.
File: the file you're trying to open.
Parameters: if you try to run an application, what parameters you want to pass to it.
Directory: Working directory.
Last param asks how you want to file to open - how the window is to open. SW_SHOWNORMAL opens it as normal and gives it focus.
Is an example of how to use it.
ShellExecute(NULL, _T("your_file_name_here"), NULL, NULL, NULL, SW_SHOWNORMAL);