This will solve all your queries

In all seriousness just follow any of the tutorials you can find in your favorite search engine. I'm sure anything that shows on the top of your search results will be more than enough to get you started.

Well I've never used Unity so I won't be able to hand out any personal recommendations. However, I don't think you're going to get your deep understanding of the program through the use of tutorials. The whole idea behind them is to demonstrate how small individual tasks can be tackled; it's then up to the reader to piece this information together and create something from all the individual tutorials.

On that note I would suggest you find any tutorial that outlines the broad scope of how an RTS/RPG game is designed. From there try and create one on your own with your own unique features. When you're absolutely stumped on how to do something specific like path finding then you can search for a tutorial on the matter and figure out how to put their code into your game. This way you're forced to alter their existing code and enforce your understanding of the subject.

If you get stuck in the tutorials and require even more information it's normally a good idea to just read through the game engines documentation. This is as bountiful as the information is going to get and you'll uncover a whole new world of functionality that you weren't going to find in any tutorials. Just monkeying around with random functions that come with the game engine will teach you most of what you need to know in due time of course.

Here's why you are having trouble:

Imagine that you've mastered game development. Seriously. You know all the languages, and they've all just blended together as a tool to get the job done. C++/Java/C#/Javascript/lua/python... whatever. Just a tool. But you're disappointed with the available tools. So one night, whilst drinking too much with your mates, you decide to create your own engine. Do things right. Create a proper game engine. Support all the platforms, allow scripting with many different languages, construct the game with a scene graph (because that's the best way to search breadth and depth and optimize batch calls), but a scene graph of component based objects, because all the inheritance is crazy.

And there you have it: Unity. A wonderful, fantastic engine that shields you from all those problems you had when you wrote your engines from scratch. The problem is, when you're new, and you have never developed something from scratch, you don't understand why it is structured the way that it is.

Long story short (too late), you need to make a lot of games and gain experience before you truly understand "why" Unity works the way it does. But you can't really understand it until you've made some games.

Sort of a "Chicken and the egg" problem. Don't worry about it. Make some games. It will come in time.