This is electrophilic substitution of benzene ring, and methyl is an electron-pushing group, which activates benzene ring and locates bromine in ortho-para (main product, meta-position).

Neither the iron nor the heater can be removed. The iron bromide obtained by the reaction of iron and bromine is the catalyst (necessary) of this reaction, which requires an anhydrous environment. Heating is to speed up the reaction.

Bromine can enter the meta position of methyl, but rarely, and the main product is ortho-para.

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