What does this quote mean? great gatsby?

It means that Nick sees in Gatsby someone who likes him in the way he, Nick, wants to be liked--in other words, it suggests total comfort. Gatsby does not try to "psych" Nick out; instead he supports Nick. Moreover, Nick also sees that the smile is doing this, that at the same time as it "works," it is a constructed gesture, so that it is part of Gatsby's self-constricted persona (Gatsby "sprang from his Platonic conception of himself").