Chlorobenzene on reaction with ${\mathrm{CH}}_3\mathrm{Cl}$ in the presence of ${\mathrm{AlCl}}_3$ will give 

The reaction can be represented as below.

As ${\mathrm{Cl}}^{-}$ group attached to benzene is ortho, para directing so it forms o-, p-chloro toluene. This is a Friedel Craft's alkylation reaction.