If you came here for the first time, the world of Arduino may be a mystery for you. Do not despair. Arduino was designed exactly for people like you. It does not matter if you have no experience in electrical engineering or programming. With a little effort, you will learn everything.
Then read about what it is and what different types of Arduino you can buy. A beginner usually buys Arduino Uno, the flagship of Arduino. The most examples are adapted to it.)
Arduino is essentially a microcontroller with complementary components. You will not be expected to build complex circuits of dozens of logic circuits around it. You do not need them. Arduino has plenty of inputs and outputs that you control using a program (called sketch) you write and send to Arduino. Programs are written in C++. You can use development environment (Arduino IDE) to create your programs.
If you've already seen Arduino, you can start reading this pages. The entire site is divided into two basic sections. The pages and the blog. Pages are oriented like Wikipedia. The individual information is organized hierarchically so that you can get from more general information to more specific. The blog uses a looser form. There you will find less expert information and you are more likely to find articles about the Arduino world or about how I gradually work on a project.
Then you will need to get an Arduino. If you are a beginner then acquire the original Arduino/Genuino Uno. The price will be 20-30 Euros. If you find it expensive and you are a little adventurer, shop on Ebay or Banggood. The prices on these stores are radically different from what someone is offering in Slovakia (or your country). Later, you can jump on the Arduino Pro Mini or you create your own Arduino out of components.
Good question. Arduino is something like a drug for whoever gets captured by it. Chinese stores offer hundreds of expansion modules for a few dollars. You can connect it all to Arduino and control it. You will not be different. You're going to be like a shopping maniac, watching for an envelope from China in your mail. And ordering what you do not necessarily need.