Getting Set Up

You need two things: the Arduino software, and telling it which board and port you have.

Install the IDE

Download the Arduino IDE (version 2.x) from arduino.cc for your system and install it like any program. It's free and open-source.

Prefer the command line? arduino-cli does everything the IDE does:

arduino-cli core update-index
arduino-cli core install arduino:avr

(Every sketch in this guide was verified with arduino-cli compiling for the Uno.)

Select your board and port

1. Plug the Uno into your computer with a USB cable. (Careful: some cheap USB cables are charge-only — no data wires. If the board powers on but no port appears, try another cable before anything else.)
2. In the IDE: Tools → Board → "Arduino Uno".
3. Tools → Port → pick the port that appeared when you plugged in (on Windows it's COM3 or similar; Mac/Linux show /dev/tty.usbmodem... or /dev/ttyUSB0).

Check: Tools → Port shows a port only while the board is plugged in. Unplug, watch it disappear, plug back in — that's how you identify the right one when several are listed.

With arduino-cli:

arduino-cli board list

Check: Your board appears with its port and name.

The sketchbook

The IDE stores your programs ("sketches") in a sketchbook folder (Documents/Arduino by default). Libraries you install also live there. Know where it is — you'll visit it when installing libraries manually.

Next: Your First Sketch