Are you just typing "su" and nothing else? There are two ways to do something with administrative rights under the terminal. There's "su" and "sudo".
Sudo looks like:
sudo chown -R adamsdv:staff *
It says "hey! do the next command as an administrative user. prompt me for the password, else use the one I typed in less than five minutes ago".
Su, on the other hand, looks like:
would ask for your root/admin password, and then you'd be acting as the root user until you explicitly said "exit" (ie. all commands you typed in would be executed with administrative privileges).
Does that help at all?