How to understand the effect of individual ingredients of recipes? I like cooking and I try different recipes from web/book. But I am not satisfied by just cooking using recipes, I want to understand what tastes individual ingredients bring to a recipe and what alternatives do I have for different ingredients of recipes that I cook so that I can experiment safely i.e replacing ingredients with there alternatives to produce slightly different taste or removing some ingredients altogether. 

Is there any resource on the web that I can consult for this? I know I can learn this by experimenting and tasting individual ingredients but I need something that can give me a starting point upon which I can build my own knowledge.
This is an overly broad question which may get closed by some here for that reason. For the future you may want to limit your questions to specifics goals or issues. It is often helpful to include what you have already tried.

As for general resources YouTube and other sites offer a variety of videos where experts will teach and demonstrate a variety of techniques. If you search Google or YouTube for "Alton Brown" and any of a variety of topics you are likely to find a video that will be helpful. Here is an episode from Alton Brown on Shish-Ka-Bob as an example.

Your profile indicates that you are in Pakistan, some of the best resources I can suggest come not directly from the internet but from television, much of which is also available via YouTube, Hulu and other internet sites. Also The Food Network website is a great resource.