V. Guillemin, S. Sternberg: Supersymmetry and Equivariant de Rham Theory (Springer 1999)
More readings:
generalities about actions: G. Bredon Introduction to Compact Transformation Groups, (Academic Press 1973)
on BB-decomposition: Andrzej Białynicki-Birula, James B. Carrell, William M. McGovern:
Algebraic Quotients. Torus Actions and Cohomology. The Adjoint Representation and the Adjoint Action.
(EMS, volume 131) [Carrell's part]