The downscaling of magnetic memory units and operational devices will soon call for functional structures with atomic precision of their architecture. But the behavior of the magnetic moments of impurities adsorbed on a metal surface is strongly influenced by the electronic properties of the contacting lead. Therefore, the comprehension of interactions between atomic spins and its solid state environment, which can be either the conduction electron continuum of the metal host, other neighboring magnetic moment adsorbed on the surface or the nearby atoms of the substrate, is a fundamental step towards the realization of the technology based on the spin degree of freedom. Since the irruption of the scanning tunneling microscopy (STM) and its different implementation modes such as scanning tunneling spectroscopy (STS) or spin polarized scanning tunneling microscopy (SP-STM), the study of spin-spin interactions at ultimate length scale is accessible. Artificially engineered Co structures built atom by atom, by means of atomic manipulation technique, adsorbed on a Ag(111) metal surface and on a Mn/W(110) metal surface with non collinear magnetic ground state have allowed us the comprehension of different interaction mechanisms between single spins and its foremost environment.