Basically what the title says, I’m a COMPLETE newbie on how to script and I need some of your advise, because you guys are experts. My friend is too lazy to explain to me what does this script do etc. , so, if you have some spare time, please help me. I want to be a game developer but, as I can’t understand and fail every time I try to code, that makes me fell sad. So, my question is: Can you explain to me what does everything do in scripting and how can I use it to make my very first game? 
While there are certainly experts here among us, the scope of your question is extremely broad. Your friends seeming “laziness” may simply be an indication that the topic is an expansive one, and one that is difficult to sum up “real quick”. A script is simply a piece of code that performs a function (and sometimes quite a few functions). This can be anything from drawing text on the screen, to counting, to moving objects, to creating & destroying objects, and much, much more. Rather than try to explain even the most basic of basics in full, please allow me to direct you to a good source of beginner’s material. Here is a link to the Unity scripting tutorials, which will guide you through basic and intermediate level programming techniques: Learn game development w/ Unity | Courses & tutorials in game design, VR, AR, & Real-time 3D | Unity Learn
You may also be interested in taking lessons at Codecademy, which has free tutorials in a variety of programming languages. Beyond that, there are a ton of great learning resources out there, including an extensive amount of Unity specific tutorials on Youtube.
If you ever find yourself stuck on a particular aspect, then feel free to ask for assistance here, however keep in mind that these forum threads are generally better suited to specific questions about specific aspects of programming and are not really designed to teach you from the ground up.
Best of luck & have fun!
“My friend is too lazy to explain to me what does this script do etc.”
A heads up: noone here will do this. Like the above post said, people here can help you with specific problems, but programming and learning to read code is something you will have to do on your own.
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Official help manual are best references for u, just read and research it everyday!
The 3 most important activities are: practice, practice and practice. 
[e] If there’s still spare time do some practice!