For developing web apps eg. oline portal, asterisk billing software, voip soft swich billing, wich programing language i should learn, please give me details.

Well, there's really 2 things to consider. First, your skill, and second, the implementation.

You could just jump right into building apps with huge web frameworks without really understanding the funamentals of programming. The problem with that is you'll lack understanding of what your doing, and if you can't find a "ready made" solution for your problem, you wont have the skill to implement it yourself. This is a very popular route to take, especially for web developers who don't actually need to do too many complicated tasks and want to get started as fast as possible.

You could also start off with a traditional "boring, old school" language, and learn about solving problems with it. And then start learning the big web technologies and whatnot. This prepares you for the problems that don't have ready made solutions. The problem with this is it's boring if your not interested in the fundamentals of programming, and it will take you longer. This is what I would recommend.

If you need to write a few pages for billing software and a portal, then the best approach is to hire a professional. Especially because your dealing with billing, and confidential information.

Nice languages to use would be the standard ones for web development, such as HTML, CSS, Javascript, PHP, MySQL, etc... The are plenty of frameworks out there to help, like Bootstrap, Codeignitor, Agile toolkit, etc. just google them.

For traditional languages for learning: Racket, Python, Java, C, C++. Some universities post there assignments online, those are usually good to follow. Take a look at MIT opencourseware. Project Euler helps get some practice in.