In this thesis, we construct a version of Morse-Bott spectral sequences for symplectic homology and equivariant symplectic homology groups. We use the spectral sequences to investigate symplectic and contact topology of the Milnor fiber and the links of weighted homogeneous polynomials. In particular we discuss an invariant of contact structures, which is called mean Euler characteristic of equivariant symplectic homology. We give some applications on exotic contact structures.