Ok we'll start with the two most difficult things first. Start steady, and find something you enjoy.
Most people coming to training as a life changer want instant change and fail because of it, the change will be for life, if you want life to be long, accept the change will be too.
Many coming to exercise late have built up a very negative view of exercise and assume they will have to do things they hate, another common reason for stopping early, if you enjoy wildlife, take long walks, beer, long walks with 2 or three stops for a half, TV, use a comfortable exercise bike or recumbent bike in front of one. The important thing at this stage is to get used to being a bit more active and healthy, not try and fix your whole like in one go.
I am going to assume you are diet controlled type 2 diabetes, the most common kind, so say that you will find it necessary to keep intensity very low and have a banana etc. within reach at all times. This isn’t something you will have to do forever, but at the start while you find your balance. If I have guessed wrong obviously let me know. If your insulin dependent, get as much professional medical advice as you can, there are many online forums that will give this, but nothing replaces a doctor who knows you.