in an aldol rxn you remove an alpha H (the H next to a carbonyl C) ... this produces a anion with a pair of electrons... using this molecule attack another molecuel of itself at the Carbonyl carbon ( the ketone portion of the other molecule) this produces a strucuter which becomes an beta hydroxy aldohyde after acid work up. With heat you furthur protonate the hydroxy molecule and that produces the final product you see ( like Cute Fairy said "its a alpha beta unsaturated Carbonyle compund")