How to make people walk?

Hello to all. I am currently a newbie at Flas MX, but i get the basics(animating basic objects,tweening,colors). But one thing i can’t get so far is how to make people seem like they are walking with their legs going right, in fornt of left, then right, so that it looks real. How would I make it so that it doesn’t just look like there just sliding? NEED HELP BIG TIME!!!