Some people (like my brother) have seen the robots on TV (Battlebots, etc.) and have suddenly gotten a 'bug' to build a robot. Not me. I've been putting off building a robot for years now. But that all changed when my brother pointed me towards the Robothon robotics competition (www.robothon.com) held in Seattle every year. Time to get building....
I rarely endorse or recommend books/companies. But I am going to make huge concessions in this tutorial.
If you want to know the nitty gritty 'how to' of robotics, take a look at Dave Cook's book Intermediate Robot Building.
If you need a quick and easy chassis, checkout Pololu's disc chassis with gear boxes and truck tires.