Only a couple of years or so ago I think the only thing on my spice "shelf" was a little jar of mixed herbs. It's grown quite a bit since then. It's strange, but to me the sight of a well stocked herb and spices shelf is the sign of a good cook, yet I"m not sure that I fit into that category yet.
Mr C is the one that has to take most of the credit for helping to expand my taste horizons and consequently my cooking abilities. When we met he was a curry lover, yet I struggled to handle a korma. Chilli was something that I used to back away from frightened.
Over time though I have definitely learnt how to use herbs and spices to transform a dish. Tonight's dinner makes use of four of the little jars from the shelf (ground cumin, ground coriander, chilli powder and ground cinnamon – in case you're interested) and hence turns what could have been a rather bland chicken dish into something very tasty.
One book that I have to admit did help me understand how best to use herbs and spices was Jamie Oliver's Cook with Jamie. There's a great section at the back of the book where he look at several common herbs and spices in turn and describes each one and the flavours it can add to a dish. This certainly helped me understand how to start experimenting. Of course, reading from a book is fine, but nothing beats actually trying the flavours for yourself.
There's still plenty for me to learn, but I'm just hoping that our new house has a bigger shelf for storing all these on than we do right now!