In two dimensional separations each peak in the 2D space is described by a "blob" whose color depends from the intensity recorded by the detector (FID, MS for GC, UV, MS, FLD for LC). Each peaks has two coordinates, the first dimension retention time,which is usually on the x axis, and the second dimension retention time, which is usually on the y axis. In "comprehensive" two dimensional chromatography methods, each peak is the result of the modulation process e.g the number of second dimension chromatograms recorded across a first dimension chromatographic peak. For more details please see the works of Tranchida et al. and Dugo et al,

This is a good book: https://www.elsevier.com/books/comprehensive-two-dimensional-gas-chromatography/ramos/978-0-444-53237-4

You can't.  It just means you have 2 peaks that are detectable under the chromatographic conditions of the GC analysis.  Even an MS detector can have 'holes' in its identification.