Carbon materials are widely employed as electrodes for electrochemical capacitors (ECs), owing to their tunable properties that govern key performance metrics such as capacitance, retention and cycle life. These properties arise from a complex interplay of porosity, structure, surface chemistry and defects, which can be optimized through targeted synthesis strategies. This tutorial reviews the major carbon-based electrode materials for SCs, focusing on physicochemical characterization techniques such as gas adsorption, X-ray diffraction, Raman spectroscopy, X-ray photoelectron spectroscopy and temperature-programmed desorption coupled with mass spectrometry. The advantages and limitations of these techniques are highlighted. Finally, structure-performance relationships are illustrated through selected case studies.