Find window

HWND FindWindowA(
  LPCSTR lpClassName,
  LPCSTR lpWindowName
);

lpClassName
window class name (registered when creating the window class name)

lpWindowName
window title

Find the specified window, the window handle is returned

void SwitchToThisWindow(
  HWND hwnd,
  BOOL fUnknown
);

hwnd
window handle to be switched

fUnknown
to true this parameter is represented using Alt / CTL + Tab key sequence to switch windows. Otherwise, this parameter should be false.

Enumerate all open windows

EnumWindows();

Find more of the same window

If there are multiple windows within the same class name of a window, such as an edit box.
Find this window can look to find the window ID with spy ++ then GetDlgItem can find the window handle of the window with ID

Child window traversal

EnumChildWindow enumerate a specified window of the child window