Originally people with type one diabetes first tested their blood sugar levels with a urine test kit. For this method you would collect a urine sample which hasn't been in your bladder for long, (so usually one hour after you last went to the toilet).
Urine blood glucose test stripsHere is a video on how to use a blood test
Then you would dip a test strip in the container of fresh urine, wait a couple of minutes, and the colour pads on the strip would change colour to show the blood sugar results.
But the test strip would only show if you were high or low on a colour chart, it couldn't give you an exact number or show if you were rising/falling.
Then came finger pricks, the more current method used to test your blood glucose levels. With finger pricks you would simply prick your finger with the prick and put some blood on a test strip.
Then put the test strip into the reader device and it will tell give you a number reading for your blood sugar levels.
The blood test strip Method is still used along side the Flash glucose monitor sometimes to make sure that the monitor has calibrated properly, and is showing accurate results.
Here is a video on how to test your blood sugar levels with the finger pricking method: