explain the grand total system at the of each song

Here's how it works.

Put all your numbers into this formula. C = Combo, P = Perfect, G = Good, A = Average, B = Boo, M = Miss.

(C * 1000) + (P * 550) + (G * 275) + (A * 55) + (B * -20) + (M * -310) = Final Score.

This is acheived by adding the points everything is worth in-game (score at bottom of screen) and then the value it is worth in the results screen. For example, Perfects are worth 50 points in-game and 500 on results when you finish the song. So every perfect is worth 550 points. Goods are 25 and 250, averages 5 and 50, etc.

Hope that's not too confusing for you.

~Squeek

Edit: If you meant Grand Total Score which appears on the menu screen and in the signature toy, that's simply the added scores on every song you've played.