Hello, I found this on KCNR's facebook page, credits to whoever made it. I really enjoyed reading it and think that it explains turfs exactly how it is in-game so I would just like this to be on the forums also instead of just on facebook.

In the latest version of Kar's Cops and Robbers, released on the 14th of March 2014, turf wars were introduced to the community. Since the release of the turf wars, Los Santos has become a battle field between the gangs of San Andreas. There are countless numbers of turf in Los Santos which are all controlled by a gang. You can now change the color of your gang, and this color will be used to represent the turfs that your gang/group has under control. You can see the gang that controls the turf by the color of the gang zone on the map. To change your group color, type '/groupcolor' or '/groupcolour' in-game. (You must be rank 5+)

When you participate in turf wars, you can have 2 roles. Defending or Attacking. Defending in turf wars means that another gang has provoked your gang on your turf, and unless you go and defend it, the turf will be taken from you and the rival gang will be in control of it. When a turf is attacked, a message is sent to all the players saying which gang has attacked which turf. The turf will then begin flashing in red on the map, to notify the gang members of which turf is being provoked. If this is your turf, you are required to go to the turf under seige and defend it from the rival gang. You will earn defence points for:
Being in the turf. (Slow defence point gain)
Shooting an attacker. (Medium defence point gain)
Killing an attacker. (High defence point gain)

The more gang members you have defending the turf, the more defence points you will earn. If your defence points are higher than the attacker's points at the end of the turf war, then your gang will remain under control of that turf and the attackers have failed to take it.

If you are Attacking in a turf war, you are attempting to gain control of another gang's turf. If there are no rival gang members online when you being attacking the turf, you will gain control of it within 1 minute. However, if there are rivals online, you must prepare to attack the gang members coming to defend their turf. You gain attack points for:
Being in the turf. (Slow attack point gain)
Shooting a defender. (Medium attack point gain)
Killing a defender. (High attack point gain)

The more gang members you have attacking the turf at one time, the more attack points will be earned. If your attack points are higher than the defender's points at the end of the turf war, your gang will override the rival gang's control of the turf, and your gang will now be in possession of that turf until another gang attempts to provoke it.

In order to begin attacking a turf, you must enter a rival gang's turf and type '/provoke'. This will alert the rival gang that their turf has been provoked, and your gang must then gather and attempt to take that turf by shooting and/or killing the defending gang. Turfs currently do not have many advantages, but more will be added.