The codes section is for the 10 codes which are used by many radio users(fire, law, ems, etc) Every agency can assign any 10 code its own meaning, so that is why you will find a bunch of different meanings for them. It will take a fair amount of listening to a scanner to figure out what each 10 code actually means in your area. Believe me, they change city by city, county by county, agency by agency.
The tone column in the DB is only necessary if #1 your scanner or radio is capable of using CTCSS or DPL tones and #2 you actually want to program them in. Their purpose is to help eliminate unwanted interference on a particular frequency. They are also used when you have multiple users on the same frequency. By changing the setting of your pl tone you can filter out all the stuff on that frequency that you don't want to hear(like another city or agency).
The GMRS/FRS radios claim to have privacy codes that allow you to keep others from talking on the frequency you are using. These "privacy codes" are actually PL tones. So if you set 2 radios to Frequency A with PL tone B, then the only way your radio will recieve anything is if another person transmits on Frequency A with Pl Tone B. The only catch is that if you have no PL tone programmed, you will get everything transmitted on the frequency(so how private are these codes).
Hope that helps! That is atleast the basics. Ask more questions if you are still uncertain or confused!!
