Though its name does not reveal it, this molecule is a relative of famous IT-moisturizer, Hyaluronic Acid. Just like HA, it is a glycosaminoglycan (aka GAG), meaning that it is a big sugar molecule from repeated subunits (what's more, one of the subunits is the same, glucuronic acid). Along with HA and other GAGs, it likes to hang out in the dermis (middle) layer of the skin where it is part of the gooey, bouncy stuff outside of the cells called extracellular matrix (ECM).
As for skincare, Sodium Chondroitin Sulfate is probably too big to go right into the dermis (though much smaller than HA with 5000-50 000 Da molecular weight), but it has a comparable water binding ability to HA (which means a crazy water binding ability) and better affinity for the skin surface. This means that it forms a nice, water-rich film on the skin bringing an immediate and strong moisturising effect.