I am a gluten for action - a couple of hours ago I learned about BitCoin, found this forum and installed the BitCoin app. I found the BitCoin package in Synaptic, and I ran it to see if there was a GUI or anything, and about a half hour later I noticed my CPU2 in overdrive and found that BitCoinD was doing something, so I killed it.
Can anybody tell me what it was doing?
bitcoind is the daemon. You won't see much of a GUI there. Did you check the wiki
on how to properly install and configure bitcoin?