In general terms stainless steels are iron based materials containing more  than 11-12 % Cr . This level of Cr makes the steel passive by forming an extremely thin continuos and stable film on the surface of the stainless steel. Nickel enhances the passivity in more aggressive conditions. Manganese has a lesser effect on the corrosion and heat resistance but modifys the mechanical and physical properties like fabricability , weldability and machinability. SS 202 is basically cheap as compared to SS 304 as there is less costly nickel content   .  The nickel content of SS 202 is 4.0/6.0 % and SS 304 is 8.0/10.0 , Cr content SS202 is 17.0/19.0 and SS 304 is 18.0/20.0 , Manganese content SS202 is 7.50/10.0 and SS304 is 2.0 .

SS 202 is basically a cheaper alternative to SS 304 for applications like kitchen sinks , utensils etc .
SS 304l is a low carbon steel  to avoid problems like intergranullar corrosion ( IGC).