Markovnikov's Rule (note spelling) is used to predict how (for example) HX, where X is a halide, adds to an unsymmetrical olefin. As the diagram below shows, Markovnikov addition follows the rule that the "H" will add to the least substituted carbon while the "X" will add to the most substituted carbon. This is due to the fact that these reactions proceed by protonaton of the olefin to yield a carbocation. Protonation at the least substituted carbon yields the most stable carbocation (in this case a secondary carbocation). Finally the carbocation reacts with $\ce{X^-}$ to yield the final product.