How to: soil moisture measurement?

Is anyone here had an experience in order to build Soil Moisture Sensor? If there any, can u share ur knowledge with me because I never do this kind of project before by using arduino. Actually my project is about to detect the soil moisture by using Vegetronix VG400 Soil Moisture Sensor probes. It will change the analog to digital value so that it can be easily determine the moisture. If the moisture too dry (RED LED blinking), if the moisture wet (GREEN LED blinking) and if the condition of the soil is not too dry and wet (YELLOW LED blinking). I also wanna make an alarm when the moisture too dry. Can somebody help me to figure it. Thank You