Basic grid/mesh generation using Autogrid.
 

Can anyone here give me a basic-level ,step by step tutorial to grid generation using Autogrid for a non-bladed channel?(It is essentially a bifurcation channel with rotational periodicity).

Autyogrid does not seem to be easily applicabale to your case.
I propose to use IGG instead.
Autogrid is solely developoed for turbomachinery applications.

regards,