how to identify sigma and pi bonds in the given structure?
Sigma bond is formed by head to head overlapping of orbitals while pi bond is formed by lateral overlapping of orbitals. When there is only one bond, it is sigma bond, if there are two bonds between atoms, one is sigma and other is pi- bond. If there are triple bonds between two atoms, then one is sigma and other two are pi-bonds.
Formation of Pi bond in ethylene