Beginning electronics programming
I've got several Arduinos, plus a couple of Raspberry Pi's.  I'm going to suggest the Arduino Mega 2560; it's got 256 KB Flash, which is plenty (way more than the Uno, which has only 32K), and 8 KB RAM, which is usually enough unless you are storing large arrays, and then you can get more RAM if you need to, like this 512 KB expansion RAM board.

Get an authentic Arduino (like the one I linked to), some of the clones are iffy.

Both the Arduinos and Raspberry Pi's are expandable through "shields", which are stackable boards that contain various hardware goodies like motor controls, relays, wireless (Bluetooth, WiFi), and LCD screens.  You can also connect wireless breadboards using male to male jumpers (see picture below).  There are hundreds of shields.  Quite a bit more for the Arduino than the Pi.

The big difference between the two is ease of use.  With the Arduino, every  time you add some hardware there is usually a library download available that includes not only the driver code but also examples programs for checking out the board and showing off features.  I just got a 3.2" LCD plus touch panel running last night in less than 15 minutes.  The programming language is C++, so each peripheral will show up as a C++ class.  There is no OS, you are programming at the bare metal.

The Raspberry Pi on the other hand runs Linux and is more like programming a PC.  It of course has gobs of storage -- for example 1 GB of RAM with the Raspberry Pi 2.  I just don't find it as accessible as the Arduinos.  I program my Raspberries in Python.

Both of these boards are small but still too big to fit inside a little toy car. However there are lots of projects for both the Arduinos and Pis for  controlling robotic vehicles.



You can see an Arduino (blue board with jumper wires sticking out of it) sitting on top.

Both Arduinos and Raspberry Pi's have their own forums here: arduino.stackexchange.com and raspberrypi.stackexchange.com.