I would advise you to get proper music lessons with a vocal coach or a guru. This cannot be taught online; you really need personal interaction.
You will have to practice scales and/or ragas thoroughly and then you will move on to songs. If you're figuring out notes on the piano, that's the very first step - associating a sound with a note. Then loads of practice and learning technicalities.
Remember that many of these contestants on Indian Idol have been singing or taking lessons for 5-10 years.
A guru can help you correct your sur for the most part. But, making it further really depends on your vocal range, voice quality and throw.
Good luck!