Plug it in
You can plug it in to your computer USB port immediately, without a problem.
A USB port gives 5V of power.
If its working correctly, then the green led comes on, indicating power is supplied, and
an orange led flashes, indicating it's resetting itself, then stays on.
5V is enough for (and is the standard for most) electronic components; equivalent to 3 'AAA' batteries, so enough to
power a torch battery, not enough to hurt you if you touch it, and also not enough to power a motor.
The connections around the edges are for plugging stuff in.
After plugging the arduino into your computer via the USB cable, you can run the Arduino IDE program on your computer.
(IDE = Integrated Development Environment).
The IDE will bring up a window; you type in computer code (a 'sketch') and upload it to the arduino. The arduino will then
run that code.
I use Linux Mint 16, and the arduino IDE was available in the software repositories for easy installation.
After a few days of tinkering, I searched online for code to use my humidity sensor. It melted.
For your first few experiments, you may want to consider using code only from the official website, http://arduino.cc.
This is my arduino plugged in to my USB port. Note that I have 2 orange LEDs because
I am running a sketch. Initial plug in should give you 1 orange LED and 1 green LED.
The best way to read it ! Get a hobby magnifying glass. I chose a hobby tool
that also has 2 flexible clips, to hold pieces together while soldering.
There's no shame in using a magnifying glass ! You will need to read the arduino board, and resistor codes,
and the numbers on many components.