Question

Explain with the help of resonating structure that phenol is Ortho para directing nature

Answer 1

Because the -OH group is a strongly activating group (see Electrophilic aromatic directing groups).  

The -OH group tends to be electron-donating because the extra electrons around the oxygen atom can be shared with the aromatic benzene ring. Thus, it contributes resonance structures that can be seen below.

As you can see, the resonance structure of the phenol molecule includes 2, 4, and 6 positions (or ortho/para positions) where those positions have a partial negative charge. This opens up these positions for possible attack by an electrophile, through the process known as electrophilic aromatic substitution.