Buy the Arduino UNO (R3 at the time of this writing). This is the “most standard” version of the Arduino that I’ve come across. The Arduino IDE works perfectly via USB and most shields that you come across will be physically and electronically (5V logic) compatible. I would start with the Arduino UNO R3 to develop on and then get a smaller or more energy efficient version when finalizing a working prototype.
The classic lighting of a LED connected with a 220Ω resistor is always a great way to start. But I think a great first project that will cover the basis of A LOT of future projects is to read input from a sensor of some sort and then output a value to a LCD display.
As a first project, I would recommend a simple, but useful temperature and humidity read out, a thermo-hygrometer with a basic 16×2 LCD display. It’s easy to be overwhelmed by all the various concepts involved when starting with electronics, but you really don’t need to understand too much to get something working. You can always dive deeper once you get a few projects under your belt.
- Arduino UNO R3
- 4x AA battery holder or similar 5V power supply
- Temperature and humidity sensor DHT11
- 16×2 LCD display