The green arrow indicated a skill has 'popped' which means it has gone up a level and stays for the week until the next training occurs. Training a skill until you get a pop is the way i do it that way i can keep there main skills pretty even so the wage doesn't get out of control. Each training also trains seconday skills but at a lower rate then the primary skill being trained. Have a look under the important threads thread in the help section it will give u more info on traing speed.