I'm no expert, but what I think I know (and I could be wrong) is this:
A dream catcher is a native american decoration created to protect people from nightmares & to facilitate good dreams.
The beads represent bad dreams being caught or trapped by the dream catcher while the feathers help transport you from the physical to the dream world...
at least that's what the people around me have said, and it made sense to me so I never really questioned it. Maybe I'm wrong and someone else has a better answer.
All I know is that they are pretty, fun to make, they are great gifts to give, and at least for my family ~ they work!