Answer
The curved arrows in the picture show the movement of electrons. $CH_3-CO-CH_3$ is the Lewis base (nucleophile) and $H_2SO_4$ is the Lewis acid (electrophile).
Work Step by Step
The lone pairs on Oxygen attack the H, and takes it. Then the bond between the H and O in $H_2SO_4$ breaks and the electrons go to O, forming $HSO_4^-$ ion. Since $CH_3-CO-CH_3$ donates a pair of electrons it is lewis base and $H_2SO_4$ accepts a pair so it is lewis acid.
