How do you draw the mechanism of bromocyclohexane?

Mechanisms apply to reactions, not to single compounds. You might draw a structure for a single compound. Cyclohexane and its derivatives can be shown in different ways depending on whether you need to show the three dimensional structure or not. If 3-d is not needed, draw 6 carbons in a ring joined by single bonds, with two hydrogens on five of them and a hydrogen and bromine on the last one. The ring is symmetrical, so it doesn't matter which carbon has the bromine.