Actually there are following four sections,
1) Elementary/primary school: 5 years
2) Secondary/high school: 5 Years
3) University/college: 6 Years (college 2 + varsity 4, add another 1/2 year if u have MS/MBA)
4) Other post secondary: 0
The above is the standard one I think. Yet, they did not created that section to know how many years it took to get a certificate. rather they wanted to know how many years you have studied in different stages of education system. You wrote 10 in the first field which generally means you studied 10 years in elementary/primary school. similarly, you studied 2 years in high school and 4 years in varsity.
Forget it bro. They must know about our education system. Personally, i saw different person fills it in different way. I hope it wont create any problem as long as total duration of study equals or greater than 16.