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.
My question is, is there any better way of debugging?"
Yes.
Your approach, "1. I complete a large script, 2. Comment everything but the portion I want to check, 3. Execute the script" is not really the best way to write any software in any language (sorry, but that's the truth.)
Do not write a large anything.  Ever.
Do this.

Decompose your problem into classes of objects.
For each class, write the class by
2a.  Outline the class, focus on the external interface, not the implementation details.
2b.  Write tests to prove that interface works.
2c.  Run the tests.  They'll fail, since you only outlined the class.
2d.  Fix the class until it passes the test.
2e.  At some points, you'll realize your class designs aren't optimal.  Refactor your design, assuring your tests still pass.
Now, write your final script.  It should be short.  All the classes have already been tested.
3a.  Outline the script.  Indeed, you can usually write the script.
3b.  Write some test cases that prove the script works.
3c.  Runt the tests.  They may pass.  You're done.
3d.  If the tests don't pass, fix things until they do.

Write many small things.  It works out much better in the long run that writing a large thing and commenting parts of it out.
Debugging a scripting language like ruby