Markovnikov's rule governs the addition of

Markonikoff's rule: When an unsymmetrical reagent is added to an unsymmetrical alkene, the negative part of the reagent is attached to the unsaturated C atom having less number of hydrogen atoms.
Thus, when HBr is added to propene, isopropyl bromide is obtained as major product.
CH₃−CH=CH₂ +HBr →CH₃− CHBr −CH₃
​Thus, bromide ion is added to middle carbon atom (having less number of H atoms) and proton is attached to terminal C atom.