So, where should I start ? Can anybody give me a path to follow that the final destination is an RPG like The Legend of Zelda: A Link to the Past ?
You said something about Tetris. How can I start with tetris? Should I use Unity2D for that? I have no idea.
As L. Spiro stated, don't start with the desired project! Perhaps even don't start with a real project at all. If you would start unprepared right into the desired project you'll get frustrated very quick due to all the unknown nitty-gritty that need to be handled, and that will definitely jeopardize the project.
Since your goal is to finish a game, using an existing not just engine but tool like Unity (or Unreal, …) is IMHO the way to go. There are plenty of (video) tutorial for Unity and Unreal. Do not just look at them but get own experience by reenacting them (do not restrict yourself on tutorials related to RPG stuff here). So you get a feeling for the tool and how things are expected to work within. After doing so for some time, start to bring in own ideas / variations. Then start an own small game project. And only after that has been finished (need not be polished but, well, playable), plan out your desired project with your then existing experience and finally go for it.
Just my 2 cents, you know