Assuming you want to programmatically bring a Windows application window to the foreground (the "top" of the Z-order), the "paper" (or documentation/tutorials) you need depends heavily on which programming language you are using.
myTextBox.Focus();
Keyboard.Focus(myTextBox);
await myControl.FocusAsync(FocusState.Programmatic);
Related search suggestions will be provided. goto windows app top
If it is currently hidden, look for the option labeled Enable always on top (or ensure Disable always on top is not selected). Assuming you want to programmatically bring a Windows