module help

I still don't feel good about module. I'm trying to practice
old exam question based on modules. Can you help? Or point
out main important good things to know well?

Thank you.



1.
Suppose R is a commutative ring with unit. Show that an
R-module M is irreducible iff it is isomorphic as an R-module
to R/I, for some maximal ideal.

2.
Suppose R is ring with unit. Prove that any quotient of a
cyclic (left) R-module is cyclic. How many simple modules
(up to isomorphism) are there for the group ring C[S_4], &
what are their dimensions?
.