When the body stops producing insulin, or it stops producing enough insulin, or when the insulin it does produce is unable to carry the glucose into the body's cells, you develop either insulin resistance or diabetes.
With the normal glucose regulating system malfunctioning, your blood glucose levels keep on increasing, and when it reaches a certain level within the blood, the body attempts to remove the problem by passing the extra glucose out of your body through the urine.
This process is termed 'glycosuria' which stands for glucose urine.
Consequently, the signs of diabetes develop and these are highlighted by the following obvious symptoms;

• the passing of large amounts of urine day and night.
  This is the body's attempt to get rid of the excess glucose in the blood
• the constant feeling of thirst most of the time, usually resulting in a dry mouth feeling, usually as a consequence of the large urine output
• excessive tiredness due to a lack of fuel (glucose) getting the actual cells that need it.
  
• drinking excessive amounts of water in response to the overwhelming thirst.
  
• Perhaps weight loss because the normal fuel glucose is unable to be made available to the cells, and therefore stores of fat are broken down
• Itchiness of the skin, and minor infections resulting from bacteria being able to thrive on the high sugar content of the urine and blood
• Blurred vision due to the effect of fluid levels in the eye.
  

An excessive blood glucose level is termed hyperglycemia meaning excessive and glycemia meaning sugar in the blood.
This is the opposite of hypoglycemia which is a dangerously low blood sugar level