It's a tutorial for windows forms positioning
In all Windows Forms controls, they there's 4 properties indicates the position of the element relatively to the parent element (i.e. Button to Form).
These are: Left, Top, Right, and Bottom, The Right and Bottom properties are Read Only, their value equals Left + Width and Top + Height respectively.
In fact they are wrappers on Location property, where Left is a wrapper on Location.X, and Top is a wrapper on Location.Y. Location Propery can be set in the propery window, and will give the same result.
The Left property (as descriped in the documentation):
An Int32 representing the distance, in pixels, between the left edge of the control and the left edge of its container's client area.
The Right is a bit different
An Int32 representing the distance, in pixels, between the right edge of the control and the left edge of its container's client area
As you see, the Right = Left + Width
The same for Top and Bottom:
Top: An Int32 representing the distance, in pixels, between the top edge of the control and the top edge of its container's client area. Bottom: An Int32 representing the distance, in pixels, between the bottom edge of the control and the top edge of its container's client area.