The Help File Says:
I moved your thread to the right forum, as this is a support question.Left side-bearing, right side-bearing, and advance width
In the Glyph Edit window there are two vertical lines (normally the glyph outline lies in between these lines) that represent the left and right side-bearings. These are shown by default but you can hide them through the Show Metrics button on the Drawing toolbar. The left and right side-bearings can be changed by dragging them to their desired position. You can also adjust the side-bearings through the Glyph Properties tool window. White space should be evenly distributed between the left and right side-bearings of glyphs except when font is specifically designed with ligatures for joining characters in a cursive script font.
FontCreator - Discussion
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