I am basically from the world of C language programming, now delving into the world of scripting languages like Ruby and Python.
I am wondering how to do debugging.
At present the steps I follow is, 

I complete a large script,
Comment everything but the portion I
want to check
Execute the script

Though it works, I am not able to debug like how I would do in, say, a VC++ environment or something like that.
My question is, is there any better way of debugging?
Note: I guess it may be a repeated question, if so, please point me to the answer.
The debugging method you described is perfect for a static language like C++, but given that the language is so different, the coding methods are similarly different. One of the big very important things in a dynamic language such as Python or Ruby is the interactive toplevel (what you get by typing, say python on the command line). This means that running a part of your program is very easy.
Even if you've written a large program before testing (which is a bad idea), it is hopefully separated into many functions. So, open up your interactive toplevel, do an import thing (for whatever thing happens to be) and then you can easily start testing your functions one by one, just calling them on the toplevel.
Of course, for a more mature project, you probably want to write out an actual test suite, and most languages have a method to do that (in Python, this is doctest and nose, don't know about other languages). At first, though, when you're writing something not particularly formal, just remember a few simple rules of debugging dynamic languages:

Start small. Don't write large programs and test them. Test each function as you write it, at least cursorily.
Use the toplevel. Running small pieces of code in a language like Python is extremely lightweight: fire up the toplevel and run it. Compare with writing a complete program and the compile-running it in, say, C++. Use that fact that you can quickly change the correctness of any function.
Debuggers are handy. But often, so are print statements. If you're only running a single function, debugging with print statements isn't that inconvenient, and also frees you from dragging along an IDE.
Debugging a scripting language like ruby