Your milking skill increases as you....milk cows!
To milk a cow, activate a container just as a jar, or flask. Find a cow and right click it. The higher your milking skill, the better QL milk you get.
Select MILK. Once you do, the jar will fill up with [[Milk]].
You can milk a cow once every 24 real life hours. However reports are that some cows can be milked once every 1 real life hour.