I suspect, by your question, that you don't just want to assemble a kit that you buy from the store, but you want to do something a bit more challenging. Perhaps the best way to really get going and have some fun quickly is to get your hands on a broken or used RC car (and its remote control), take it apart and re-use the electronics and motors within your own custom chassis. In this way, you aren't biting off more than you can chew. Building a chassis and body that actually works is pretty challenging, and you won't be faced with the electronics complexities to start with.
Ron is correct. The mechanical aspect of RC design is much more challenging than the electrical portion.
See image below of my custom built Nitro dragster. The electronics were simple servos and a rx unit. The rest was the hard part. Also, be advised that building your own RC will cost quite a bit.