This is how I understand it simply: A Raag is a set of rules for creating music/melody.
The rules of a Raag will determine things like:
* which notes to skip and which notes to use – overall
* which notes to skip and which notes to use when you’re ascending from low to high
* which notes to skip and which notes to use when you’re descending from high to low
* what pattern of notes must be included in the music you’re creating
* what pattern of notes must be avoided in the music you’re creating
* which notes you can emphasize (hold longer – extend)
* which notes not to emphasize (just touch that note and move on)
I have also seen documentaries where Great Masters ask their students to pay attention to
* volume control : which notes can be played loud , which notes should be played softly – to enhance the effect of the Raag
Staying within the rules of each Raag – you can improvise as much as you wish.
That’s basically it.
I have learned that it’s commonly accepted that Raags have a prescribed time interval during the day/night during which they are ‘best’ played/sung/heard.
Personally, I do agree with the system somewhat because I have felt the amplified impact when Raags are played at the ‘correct’ times. But then again it could be because of my mood at the time, because I have also played/sung/listened to Raags at the ‘WRONG’ time and thoroughly enjoyed the experience.