How does this code work...

[CyberCarsten]

I got the following code from parksie, that had a messagebox show the Windows Dir.
But I don't understand what the first line does:

The first line:

TCHAR pcBuf[MAX_PATH];

The entire code:

TCHAR pcBuf[MAX_PATH];
	GetWindowsDirectory(pcBuf, MAX_PATH);
	MessageBox(pcBuf, "Windows folder!", MB_OK);