It's sounds silly, but just get an UNO, a breadboard, wires, 1 resistor (220 ohm) and an LED.
Wire up a LED circuit, and program the Arduino to flash the LED.
(There's a million examples of this all over the internet).
Without getting into any sort of heavy circuits or complex programming, you'll have a quick stress-free introduction to Arduino.
This will teach you:
- using a breadboard
- wiring digital ports on the Arduino
- polarity of components (LED yes, Resistor no)
- using the Arduino IDE
- uploading to the board
This is a great jumping-in point because it's reasonably fool-proof.
Sure you can eventually be PID-controlling the balance of a 2-wheel robot. But build yourself a working foundation of good knowledge first.