An acyl chloride is a basically a carbon atom with a double bond with oxygen, single bond with chlorine and any other functional group. The halogen carrier basically accepts the chlorine atom temporarily which allows the remaining compound to react with a benzene ring with an electrophilic substitution reaction. At the end of this the carbon attached to the benzene ring will have a double bond with oxygen as this is the carbon which has a positive charge after the loss of chlorine atom which is only 2 and 3. The hydrogen lost by the benzene ring for this substitution accepts the chlorine atom from the halogen carrier that is temporarily holding it forming HCL basically. If you need to know how to draw the mechanism I would search this up online or ask your teacher to make sure you get it right.