Porsche 906 was a Group 4 vehicle, later Group 4 became Group B.

According to Wiki it was in Group 4 & modified for Group 6
http://en.wikipedia.org/wiki/Porsche_906

do you know what group is belongs to bro?

It's a Porsche 906 Carrera
As seen here:- http://www.imcdb.org/vehicle_18359-Porsche-906-Carrera-1966.html

http://www.youtube.com/watch?v=Eiv2y8GgUMg&feature=related

Pause at 3:36. What car is that and which group does it belong to in the past and present?

Example, in the past they call it Group 6, now it's Group C.

Much appreciated