how Na2O acts as both oxidising as well as reducing agent.......but Na2O2 don`t?

In Na2O  the oxygen atom loses one-two electrons to form a bond with two Na atoms, so it will act as an oxidising agent and it will also gain two electrons from Na atom to obtain octet configuration, so it will act as a reducing agent.
In simple, the substance which loses an electron from the oxygen atom will be considered as an oxidising agent or it can also be termed as a reductant.
And the substance which gains an electron to oxygen atom will be considered as a reducing agent or it can also be termed as an oxidant.

 

In the oxygen atom loses one-two electrons to form a bond with two Na atoms, so it will act as an oxidising agent and it will also gain two electrons from Na atom to obtain octet configuration, so it will act as a reducing agent.