There are a number of applications to make windows stay on top so they're always in view, and DeskPins is a simple and intuitive addition.
Installation is quick and when started, DeskPins puts a little icon in the system tray. When you want a window to stay always on top, clicking on the icon turns your cursor into a pin which you simple left click onto a window to attach the pin. Your window will now stay on top of all the rest.
You have unlimited pins, so you can have multiple windows on top. Multiple pinned windows will act like normal windows in relation to each other, while always staying on top of unpinned windows.
There's nothing more to DeskPins than that. It's really light on system resources, and couldn't be more intuitive.