1)first prove it for 1 assuming it to be true for n.
2)then prove it for 2 .
3)Now prove it for n+1.
4)while proving for n+1, substitute values you got for n which was assumed to be true earlier.
5)if this results into the relation being true for n+1 then you are done.
speaking frankly i never understood how this is a proof. perhaps it shows that since for every n and n+1 the relation is true therefore it is true for all natural numbers. natural numbers progress uniformly. so perhaps like that!