When you watch a video in VLC full screen, the controller bar is the one with the play and stop buttons on it. It is usually shown at the bottom of the video screen. It only becomes visible if you move your mouse during video playback.
Did you know you could click on that bar and drag it to anywhere on that screen? And if you have a dual monitor setup, you can play your video in full-screen mode on one monitor and drag the control bar to your second monitor. (It doesn’t stay there, though– once it fades it returns to the video.) If you want to keep it there, just keep your mouse on it so it doesn’t fade out.
But you can also lock it in place at the bottom of the screen. VLC refers to this as Docking and Undocking.
I believe it’s undocked by default. To dock it, or lock it in place at the bottom of the screen, click on the icon which is usually down by the volume control– the two-headed arrow.
To undock it, just click it again. So, click to dock and click again to undock.