Star formation and quenching are two of the most important processes ingalaxy formation and evolution. We explore in the local Universe theinterrelationships among key integrated galaxy properties, including stellarmass $M_*$, star formation rate (SFR), specific SFR (sSFR), molecular gas mass$M_{\rm H_2}$, star formation efficiency (SFE) of the molecular gas andmolecular gas to stellar mass ratio $\mu$. We aim to identify the mostfundamental scaling relations among these key galaxy properties and theirinterrelationships. We show the integrated $M_{\rm H_2}$-SFR, SFR-$M_*$ and$M_{\rm H_2}$-$M_*$ relation can be simply transformed from the $\mu$-sSFR,SFE-$\mu$ and SFE-sSFR relation, respectively. The transformation, inprinciple, can increase or decrease the scatter of each relation.Interestingly, we find the latter three relations all have significantlysmaller scatter than the former three corresponding relations. We show theprobability to achieve the observed small scatter by accident is extremelyclose to zero. This suggests that the smaller scatters of the latter threerelations are driven by a more fundamental physical connection among thesequantities. We then show the large scatters in the former relations are due totheir systematic dependence on other galaxy properties, and on star formationand quenching process. We propose the sSFR-$\mu$-SFE relation as theFundamental Formation Relation (FFR), which governs the star formation andquenching process, and provides a simple framework to study galaxy evolution.Other scaling relations, including integrated Kennicutt-Schmidt law,star-forming main sequence and molecular gas main sequence, can all be derivedfrom the FFR.