What is the main differences between a spinning reel and a baitcasting reel?

I just returned from a fishing trip and caught 4 bass on my shimano spinning rod/reel. What are the main differences between a spinning reel and a bait-casting reel? Which is better? What are the advantages of each? Thanks

A spinning reel has a fixed spool meaning that the spool remains stationary and the bail wraps the line onto the spool. In a baitcasting reel, the spool rotates to dispense and retreive the line. I was always taught that you use a baitcasting reel for heavier lines and a spinning reel for lighter lines.

Which is better is personal opinion.

Some of the advantages to a spinning reel are:
They are easier for a beginner to learn and use.
There is a far less chance of a birds nest with a spinning reel. Baitcasting reels can run into backlash or overrun, especially in the hands of someone with a bit less experience, because of the way the reels work. You must control the spool while you are casting or you run into problems. There are some new technologies today that help in that regard.
You can throw smaller lures more easily.

The advantages to bait casting reels:
Increased casting distance.
More sensitive drag systems

SHIMANO ROD AND REEL REVIEWS