A glucagon injection is used when somebody has a low blood sugar emergency and needs to increase their glucose levels immediately. 
Glucagon injections cannot be prepared ahead of time as their usefulness quickly wears off, so you will need to create one at the time of use. You should have two kits available in case you need a second one for any reason. You will also want to regularly check the expiration dates of your kits to ensure that the glucagon is still good.
Note that if you discover somebody who is unconscious and believe that low blood sugar may be the reason, do not hesitate in giving a glucagon injection as no harm will be done with a needless glucagon injection, but not giving one to somebody who needs it is dangerous. You will want to give a second injection and call for help within 10 minutes if the first one has not helped as a coma or seizures may result from continued insulin issues.
People also use this shot if they are conscious but cannot take glucagon into their body by mouth for any reason such as being ill and not being able to keep any food or liquids down.
The kit is relatively easy to use, but it is important to carefully follow the directions and ask for assistance if necessary.
When it is used, a powder substance that contains glucagon interacts with a liquid-filled syringe. The amount that is used depends on the person being injected. In most cases, a milligram is recommended, but follow the instructions given by a doctor or that were provided with the kit if they contradict.
Afterwards, speak with a doctor to determine what had caused a glucagon injection to be necessary in order to avoid repeating it in the future.