With those programs u can look inside of each packet that enters your nic card, or leaves, and look inside of the frame's of the packet for items such as destination IP, host IP, protocol being used, etc.... they are powerful tools.
The negative numbers are the signal strength expressed as a dB ratio relative to a reference level. So a negative number is merely telling you how many dBs less than the reference level the signal is. This kind of measurement is common when dealing with RF, but don't worry about it. Just remember that the bigger the negative number, the weaker the signal.