Organic molecules experience appealing applications in the industry of electronic devices. The key to developing the functionality of these applications lies in the thorough understanding of the electronic structure of the employed molecules and their interactions with the unavoidable surfaces. In the first part of this thesis, state-of-the-art density functional theory (DFT) calculations in close collaboration with experiment have been presented to exemplary address the on-surface structure formation in the prototypical (i) perylene-based diindenoperylene molecule (DIP) on a reactive surface and in (ii) a functional molecule with a nonuniform internal charge distribution, namely the perylene-3,4,9,10-tetracarboxylic diahydride(PTCDA), on ionic surfaces. For both systems, the adsorption mechanisms have been rationalised and compared. The second part of this thesis presents a DFT-guided multi-technique investigation on the interfacial chemistry of a macrocyclic low-symmetry molecule, namely the free-base5,10,15-tris(pentafluorophenyl)corroles (H3TpFPC), adsorbed on Ag(111). Combining structural modelling with high-level calculations of relevant X-ray core-levels and absorption edges, a detailed insight into the complex on-surface chemistry of corroles has been achieved. Beside corroborating the on-surface reactions and providing valuable information on the geometries of corrolic species, it is demonstrated that theory-assisted near edge X-ray absorption fine-structure (NEXAFS) spectroscopy enables the site-sensitive monitoring of on-surface chemical reactions, thus, providing information not accessible by other techniques.