Most of the flavors come from grains or other things added to the boil (honey/molasses/etc), not the fermentation. More typical "after fermentation flavors" come from things like fruit, oak, vanilla, bourbon, etc. Spending countless hours reading on here and experimenting with different grains has helped me a learn a lot. Keep in mind that it is easy to go overboard on some of the grains such as Caramel. There is lots of information on here as to what flavors different grains will impart on your beer.
If you have specific flavors you are trying to get I am sure people here could help guide you to the best way to achieve that.