How to begin?

I want to start with Arduino, i ordered Arduino Uno R3 (not clone) for cca 23 euros. So, what do i need to begin? Can you write me some useful electric components and shields that are good for beginning?

Any starter kit would do.
You should have asked before, because you would have saved some money (at least for shipping) by ordering a kit that includes an Uno.

To give the best answer, the best question has to be asked.
What are your goals with Arduino ?

I know, but i really don't know goals... First i want to improve my skills in electronic, later i want to build some projects, maybe some robots, car...

How are you going about improving your skills with electronics?

Make some circuits on breadboard, making some projects using microcontroller... I'm really good at programming (for Windows and Linux), but haven't done anything like programming microcontroller, so i wanna start with Arduino and making some basics PCBs... I know basics electronic theory about circuits, about resistors, capacitors, diodes, transistors, ICs, i have a lot exp in repairing computers, and have some exp in repairing others electronic devices (amplifier, TVs etc.) but now i want to start my own projects.

What are Kirchoff’s voltage and current laws? What is a Thevenized circuit, and a Nortonized circuit, and why do we use them? What are the major differences between BJT and MOSFET?

If you really want to learn electronics, get a few general purpose shields with protoboard.

Also, get a large protoboard. Build some stand-alone circuits.

Depending on where you would put your experience level, there is a 'Multifunctional Expansion Board' available on eBay from several sellers. Simple but lots of things to do without the wires.