Can we use peaks in any chromatogram to identify a compound
Compounds have specific retention times that are used to identify their respective peaks in chromatograms. Usually these times are dependent on many factors (temperature, column type, mobile phase...), and as such some kind of pre-calibration of the machine with respect to compounds in the mixture has to be done. The area of the peak is then indicative of the amount of substance, also subject to calibration (or comparison with reference substances with known concentrations).

For structure elucidation of previously unknown compounds in mixtures other methods such as GC-MS are much better suited.