Welcome to the forum, Spicedumb.
Learning which herbs & spices work with which foods, and with each other, is a never-ending thing. Everytime I cook something I learn a little more.
I suggest two things. First, get you some cookbooks that deal specifically with the topic. Choose them carefully, though. I don't think you want, so much, herb & spice guidebooks, as cookbooks that use them in various ways.
One I can recommend is Ana Sortun's "Spice. Flavors of the Eastern Mediterranean." What she does is arrange her recipes by their major spice elements. Along the way she explains why those work together, and so on.
Second: Read my thread in the cooking school forum about training through repitition. It your case the idea isn't so much to learn cooking techniques, as to see what happens when you use particular herbs and spices. By ringing the changes on a particular dish, and just changing the herbs & speices used, you'll quickly develop a feel for how to use them.