Start by clicking on "Robot Tutorial" in the upper right corner of this page. Lots of basics to get you started.
Next browse and read through the many threads in these forums. Then go the the links listed in those threads and read more. Googe/Wiki search for terms and other info you don't understand.
Also, Pololu, Adafruit and SparkFun have some good beginner info and tutorials about different sensors. These are well worth reading.