If you want to find out the protein backbone dihedral angles, you can use the Protein Report tool. Just click on the Protein Report button, the Psi, Phi, and Omega angles will be calculated for each residue along the amino acid chain, and stored as properties of the residue in the AminoAcid tab in Data Table of the Molecule.
For a graphical representation, use the menu command Chart > Ramachandran Plot, to generate the Psi Phi plot.