ProMods

Not sure what's the appropriate name but I hope you understand what I'm asking. The highway is example A7 and I want it to show on the map.

You need to create a Map Overlay

How?

Again - if you want to be a successful modder, you just can't ask such questions...
Check existing files. You got a hint it has to be an overlay. So you know where to look for. Check SCS overlays and create a new one. You have to understand it. And you won't understand, if you won't try yourself. Modding isn't about following tutorials step by step, especially that there are no tutorials for many things and you have to discover stuff yourself. Check existing things, experiment, fail 10 times to finally succeed. Asking such basic questions will lead you nowhere. The earlier you get it, the better you'll be in the future, when you learn how things work in ETS

Have you forgot that besides the dds file there's a tobj file and a mat file? How am I supposed to that? That's the actual problem not the Overlay itself. I do want to do things myself but it's nice to have someone who would teach me a lesson or two not fucking leave me hanging. Sorry for acting like this but I had a really bad day.

Same opinion as Voytek.
First time I opened the editor I said: "WHAT?!"
But after experimenting and failing and and and...
Meanwhile i fully understand the editor. You can check out my Italy Sign Project
I recommend you look first some Tutorials (e.g. Arayas)
And then try and experiment yourself in the editor.
Asking Question won't really help you...

I know how to make road signs.

No, I mean how my quality was at the beginning and now...

Sorry. It's just I want to do something useful for once. But instead I made things worse. Even my closest friends think my project is too much for me.

If it's too much and everybody says that, maybe it's better to listen and not push yourself and stress because of that...
It's supposed to be fun and satisfying for you.

Of course, an overlay consists of few files. If you know that, where's the problem?

As I said, check for existing files, find them all and make your files in a similar way. That's how we all started.
Imagine you're the first ever modder in 2012 after the game release - would you be stuck like today, because you would wait for an easy answer? There would be nobody to tell you anything. Modding is about looking for answers yourself. No idea how to encourage you more.