There are different ways of building a robot. For your requirement, do the following:
1. Decide on a microcontroller. AVR, PIC or any other microcontroller
2. You can use arduino, but that does not give you a solid start as it is more of plug and play. If you need less to learn, but kick start in robotics, go, give it a try.
3. Next learn how to program your microcontroller. Even if you know C or C++, programming for microcontrollers is different than programming in a PC.
4. Register in some robotic forums and get the community help.
5. Learn about sensors and actuators used in robots.
Lastly, start making robots today rather than waiting for gathering more and more knowledge. You need to get your hands dirty to learn quickly.