It puts the second job back in the foreground and you will have to wait for the job to finish to get your prompt back. ( or do Ctrl+Z and bg again )
So in a nutshell, the "&" sign at the end of a command puts it in the background, you get a job number and with that job number you can with "fg %<jobnumber>" and "bg %<jobnumber>" put it back and forth.
Now, there are some restrictions:
1). There should no input needed from the keyboad for the background process.
2). Better send output from the process to a file and not to the screen.
3). If you exit the shell the process is stopped ( you can prevent this by preceeding the command with "nohup" )
-- Sep 20 2005 ( Revised Dec 10 2005 ) --