It is possible to learn to program without taking a course, but you need very good aptitude for it. Blowing my horn here a bit:- I taught myself Basic when I was in 8th grade. I taught myself C++ in the final year of my bachelor's degree. I taught myself Java
around 2000. The more languages you learn the easier it gets. However, at the same time, when I was in 8th grade, I would try to teach other people Basic, and they won't get it. It wasn't the problem with the language itself, but the problem was that they didn't have the kind of meta-thinking that makes a programmer a programmer. I used to think that I was born with that skill, but that's not completely true. Being able to think like a programmer is a teachable skill, however, it requires a lot more hard work, dedication and, yes, money to learn it.
It's just like everything else. Olympic class athletes are generally born with an aptitude for their sport. It requires a lot of dedication and training to reach Olympic level. However, for someone who is not born with it, they can get there if they work much harder, and is most likely to drop out after reaching a certain amount of success. Programming is no differrent. You are a mental gymnast. Either your brain is wired to program or it's not. Even if it's not, your brain is plastic; with practice, and hard work, you can mold it
So, my suggestion for any person who wants to be a programmer is:- Just try it. You might be lucky enough to be born with that skill. You just might be the next Steve Wozniak or Bill Gates, or you may not be. If not, atleast you know what you need to do. Don't get dejected by failure. You will fall before you walk. One good thing about the industry right now is even if you are modestly successful as a programmer, you are still pretty successful in the traditional sense. No one has heard of a starving programmer. In the US, an "average" programmer starts earning 6 figures in a decade. If you can keep at it, barring calamaties, you and your children aren't going to go hungry
To answer your specific questions
1. How and where i should start learning these languages. Which language i should learn first and then next?? I don’t wanna pay any dollar to buy any language course so is it possible to learn through internet i mean youtube videos.
Initial language selection depends a lot on aptitude and interest. It's hard to give a reccomendation without knowing you. Visual Basic is a good place to start. Java can be too, if you have the aptitude. Or you might even try Python/Ruby on rails. I would suggest you give a few languages and try and see what clicks.
2. Which is most demanded and valuable language that will help me in my career?? ( well i’m hearing about .NET)
Languages come and go. RIght now, I beleive it's Java and .NET. However, don;t want to start a language war
You are young. You are better off focusing on learning to program. Once you learn one language, other languages come easier.
3. Is it necassary to know about background of language i mean all terminologies of relative language for making a complete application or it doesn’t matter we can make complete software without getting all infomation about language.
Language is a tool. You need to learn the tool to use it. For languages like Java, there are lot of things you need to learn. Don;t try to learn everything in one go. Take baby steps.
Having said that, learning a tool is one thing, learning how the tool works is another. This is where education is very important. You can pretty much learn to program by just learning the language. However, good education gives you the fundamentals to use the tool effectively.