Hi
@Massey61 and welcome to the forum. You are not the first, and won't be the last to be given a prediabetes diagnosis and then left to wonder what it is all about!
First off the simple stuff. Your system runs on glucose. It is generated by various routes and gets absorbed in your blood stream which carries it around your body. This allows all your systems to access it so that they will function. Too little glucose in your blood and the system collapses. Too much glucose and the system gets damaged and also might collapse. The human body has an inbuilt way for keeping blood glucose neither too high or too low so that all is well. When this system starts to underperform, then the blood glucose level tends to get higher than is wise, and that is what is called diabetes.
How is it diagnosed? Normally done on the basis of something called a HbA1c test. This is a blood test which returns a number normally between 30 and 40. The higher the number the harder your system is finding it to control the upper limit of your blood glucose. The guidelines say that once this number exceeds 48, then a diagnosis of diabetes is given and actions put in place to reduce it. The actions depend very much on how high the number is. When it gets close to 100 or above then it should set alarm bells ringing because the long term consequences of not getting it down are something best avoided.
One of the characteristics of HbA1c is that when they start to rise, they will continue to do so. Not an absolute rule but something to be aware of. It is for that reason the idea of prediabetes was introduced. If your HbA1c is below 48 but above 42, then you are given the prediabetes label. It is a warning flag which is saying start thinking now to avoid problems for later.
One of my bugbears is that everybody with elevated HbA1c levels is dumped into the same Type2 box, no matter what the reason for it. So maybe you have some fat build up in the wrong places, maybe your pancreas is not working as well as it used to or maybe the mechanism whereby glucose is absorbed from the blood is impaired. You can be fit, active and eat "healthily" and still be prediabetic. Whatever is going on, it is all treated the same.
Hope that gives you some background. The prediabetes label means you do not have to panic. What it is saying is that a few simple changes now might eliminate problems down the line. If you read around the forum you will find a lot of emphasis on reducing carbohydrate in the diet as a means of controlling blood glucose. Small tweaks are generally sufficient for somebody at the prediabetes level - the heavy lifting is only needed if your HbA1c is up in the red zone.
Read around and ask questions is the message!