Solar neutrinos are unique probes for understanding the properties of the Sun and the hydrogen-burning mechanisms which power stars for most of their lives. Over its 14 years of data taking, the Borexino experiment accurately determined the fluxes of neutrinos produced in the core of the Sun. The measurements offer an unprecedented amount of information for testing solar models. In particular, the measurement of CNO neutrinos is extremely valuable in the context of the current solar composition problem thanks to the direct link between the CNO flux and the abundance of carbon and nitrogen in the core. In this contribution we will discuss the implications of solar neutrino measurements for solar physics and highlight the role of Borexino results in testing our understanding of the Sun.