If you have a Glucagon kit, it has very explicit instructions inside the case of what exactly to do. We have never had to use it on our son, and were only very briefly told about it but never shown it open, and it was some months after diagnosis that I actually opened it and looked at it in some detail. It may well be worth you and OH doing that now. I have to admit I was shocked at the size of the needle.
As Redkite said, it has to be mixed first. I am not sure how efficient I would be in an emergency, I tend to get the violent shakes, so could be interesting if and when I ever had to do it!
What I did do was wait until our kit was close to expiry, ordered a new kit, then experimented with mixing the old one so I knew what to do. So I am now at least armed with the knowledge.......