Hello,
I think this question has been asked a lot already, but I'm going to buy the Arduino UNO, but I'd like to ask what the best way is to learn Arduino, and what else I could buy, then I can buy the board and maybe additional Leds or something too. So are there any books or guides/tutorial series that I can follow to understand how arduino works? I'm actually completely new to arduino.
Thanks in advance! 
You could start with my book
Arduino for Teens,
get you up to speed on a lot of stuff.
Get a kit, not just the Uno. Most kits come with a selection of components, a breadboard, and more importantly, a booklet that includes example circuits and sketches (programs) for the beginner. Work your way through those examples to gain some understanding of the Arduino and the sort of things you can do with it.
Could you give me some examples of those kits, which kits there are available, would help me a lot!
Hi Xirzonas!
I have bought the "official" starter-kit, wich can be found here on this site in the shop:
you have all the stuff you need, to build your first projects and everything works fine. great kit!
unfortunalety it is not available in english atm. perhaps you can buy it from somewhere else.
Here is another starter kit.
Adafruit also has some great tutorials.
http://learn.adafruit.com
Teens book is great.
Try:
http://www.amazon.ca/Arduino-Cookbook-Michael-Margolis-ebook/dp/B004KKXYPE
I would like to echo Henry_Best...
A starter kit is the best way. It will provide all the components, sample code and explanations.
A really nice starter kit is put together by Vilros and is available at Amazon.com along with the Arduino Uno Rev 3.
http://www.amazon.com/Arduino-Ultimate-Starter-Includes-Instruction/dp/B00BT0NDB8/ref=sr_1_1?ie=UTF8&qid=1392863953&sr=8-1&keywords=arduino+ultimate+starter+kit
It has a VERY nice color brochure. Clear in its explanations. Really work through it. Figure out all the code and electronics. Create your own variations of the program. Use the internet for anything you want to learn more about. Then when you want more depth go to Arduino for Teens by Robert and Kathleen Patterson or Jeremy Blum's book Exploring Arduino.
YOU'RE GOING TO HAVE A BLAST!
So actually the best way to learn, is by reading books I guess, and buying a kit.
I have a list of books, do you guys know if they're good?
I'd like to learn a lot, so not only a little programming, I want to start projects with making robots, since I'm gonna study IT and robotics next year, and I already want to understand how everything works with Arduino, so I can build my own robots.
Pauly:
Here is another starter kit.
Pololu - SparkFun Starter Kit for Arduino-Compatible RedBoard
Adafruit also has some great tutorials.
http://learn.adafruit.com
I'll add the starter kit I got from Sparkfunhttp:/sparkfun.com is a good start.