When you have a glucose test, you have to fast and then drink some stuff and wait an hour and then they take blood. There's also a 3 hour glucose test. I think with the insulin test you have to fast and give blood.
A glucose test measures the amount of sugar/glucose in your blood. Insulin is thing that transports the sugar from your blood to your cells so they are nourished. An insulin test will determine whether or not your pancreas is making insulin. Hope that helps.
By the way...
Having extra insulin is a sign of insulin resistance which may lead to type 2 diabetes, high glucose levels show insulin resistance, type 2 or pcos. Limit the refined carbs to lower glucose.