I want advice on what should I show to the employer when he asks for 'concrete and solid examples' of my skills? I am not an 'Open source enthusiast' and do not have any code implemented and flying on net. I just used to do regular assignment while at college and regular tasks while at work.
Well, just like an artist's portfolio, you have to have work created that you can show. If you don't have any work that you have (e.g., due to licensing, restrictions, work-for-hire ownership, or security issues) than just like an artist, you have to create a demo.
3D artists create a demo reel for this purpose. Designers create looking portfolios for this purpose. You aren't the first person to be asked this question: http://www.codinghorror.com/blog/2004/10/a-programmers-portfolio.html :)
Consider your audience, why they are looking at your code or examples, and what you are trying to accomplish with it. Also realize that for interviewing with a non-technical staff, they might not be able to understand nuances of code changes or architectural approach, but instead will better understand an actual program or application they can interact with and review.
So go create a few examples, that show your capabilities and perhaps your style in approaching a problem or way of thinking about solving something of interest to you.
Depending on your level, they might just want to see that you can create a window with a menu bar and check boxes. Others might be looking for deep understanding of 3D engines and modeling or experience in a particular business domain, and the programming examples are just about having a program that does things to data (e.g., parsing a datafile from a data warehouse or sample file and reformatting it in a particular format).
A friend and I were just discussing this very subject once, noting that in the future employers won't be asking what can you do, but what did you do, and look to those open source projects that indicate code checked in, programs designed, participation in teams, etc. Closed and proprietary programs won't be as reliable to indicate individual skill sets - for that you go ask a company to work for you. Best of luck!
When interviewing people, we have a very simple set of things we want to see that demonstrated:
The basic thesis is that you literally show us the code, ideally including history and discussion. Real world code is perfect, but we take into account things like CS projects and other code that people publish.
Those are the easiest ways to give concrete proof. If I can read your code, I can see that concrete evidence - even if it is just the source code behind a school project.
Beyond that, look at building a portfolio: if you have worked on closed source code where someone can run the product, point to that and explain what you did.
Failing that, you have to fall back on giving a concrete explanation that includes enough detail that I can believe what you claim. For example, talk about the exact parts of what you did - not "we" did, not "the team" did, things that you specifically did in the project.
You should expect to be answering detailed technical and/or social questions designed to drag out proof that you really understood what you knew.