Showing with your model is easiest.
Use the Rotate tool. Either hit the Up arrow to lock the rotation around the blue direction or hold Shift until you click for the center of rotation. Zoom in so you can see what you are doing and then look for the On Red… inference message.
By the way, I think you want to fix the legs. It looks like you made one and made it a component. Then you opened the component for editing and copied the geometry.
It should probably be arranged this way. Maybe the leg on the left should also have a groove?