The most common solvent is water. Why? For a start it covers 2/3 of the planet. Water is an exceptionally good solvent for ionic species, because it can solvate ions to form #Na^+(aq)# and #Cl^(-)(aq)#.
The #(aq)# designation refers to the aquated ion; in solution this means the ion is surrounded by, or aquated by approx. 6 water molecules, i.e. #[Na(OH_2)_6]^+#. Water is exceptionally good at dissolving SOME ionic species because it can solvate ions; but some ion pairs i.e #AgCl# have little solubility in water. Water is conceived to have a partially negative central oxygen atom, bound to partially positive hydrogen atoms. This charge separation is referred to as polarity and allows ion solvation, and water is the best example of a polar solvent.
Hexanes is a non-polar solvent. Hexanes will dissolve ethanol (#C_2H_5OH#), but not methanol (#H_3COH#). Why not?