It may be better for you to start out at the home page:
http://setiathome.berkeley.edu/index.html
Basically Seti@Home is an attempt at discovering ET by analysing radio frequencies across the sky (the web pages do a much better and more thorough job explaining it). Then, breaking up all that data into approx. 330K chunks and distributing a chunk to one of several million participating computers for analysis (1 chunk = 1 "Work Unit"). The remote computers do the analysis (Fast Fourier Transforms, etc.) to look for signs of ET, then return the results and recieve a new chunk for data crunching.
On the page I posted, "Results Recieved" is a count of completed Work Units (or chunks), "Total CPU Time" is (obviously) how long your computer(s) took to process thosw work units, and "Average" is pretty self-explainitory.
"Plenty of room to spare" is just that the group is actually well over 20K work units (not currently displayed but should be updated soon).