Stereo AM/FM Concept?
As Olin says, stereo FM is quite a complex project for someone just starting out with electronics.
Mono FM transmits an L+R signal in the first 15kHz of it's bandwidth. For the stereo, it involves transmitting a L-R signal above this (mono receivers only look at the first 15kHz) and then recovering each channel by (L+R) + (L-R) = 2L, and (L+R) - (L-R) = 2R.
There is also a pilot tone to indicate the stereo channel and some other stuff involved. This link will give you an idea of what you need to know.