Question: What is the purpose of using an insulin?

Emilie Combet answered on 14 Mar 2014:

Insulin is a hormone produced by the pancreas. We need it to let the glucose (sugar) in our blood enter our cells (like the muscle cells, for example). The glucose fuels the cells (it provides energy).
Without insulin, the blood glucose rises beyond the normal range, and this is dangerous. Moreover, the cells are not receiving their fuel.

People with type 1 diabetes cannot make insulin, and they need to inject it (often with a syringe and needle) instead
People with type 2 diabetes have difficulty either 1) producing enough of the insulin, and/or 2) “read” the signal of the insulin, telling the glucose to enter the cell. As a result, they need to change their lifestyle to make sure that the “signal reading” improves.