When to use int main and void main function?

sir, i have doubt related int main and void main function. i have not clearity that when to use int main and when void main function. i used these above function in two separate programs and got the same result.
some time i use return 0; function and some time not but gives the results.

actually sir, i do not know when to use these function and when not??
pls answer to clear my doubt…