Observe what the recipes are in your brewery and taste the finished beer. This will help you understand how the various ingredients and process create the flavors.
Also, read recipes on various forums. You will quickly see that there are lots of ways to approach the same "style" of beer. If you have the opportunity, make some small batches (20l or less) to try out different malt/hop/yeast combinations.
Fundamentally, you are making a soup. Think of grain as the "flavor" of the soup. Think of hops as the "spice" of that soup. They can work together to bring out the best in each other and when the occasion calls, the soup can be very "Spicy."
A solid place to start learning the relationship between ingredients and flavors is with the book "Brewing Classic Styles," by Jamil Zainascheff. There are many, many others, too, but this one is a direct line between a recipe and beer style.