Specify the "X" coordinate that represents the number of pixels the control should be from the left side of the pane. You can also click and drag the control to the exact location in the pane, and this coordinate will update accordingly.
TIP: | You can use this property, along with the Y property, to easily line up a group of controls. Click and drag one control to where it should be located, then copy its X property value to the other controls to line them up vertically or its Y property value to line them up horizontally. |