Ketosis

This is almost like a course: https://www.dietdoctor.com/low-carb Read it at your own pace and come back here with any questions. Being "in ketosis" is, of course, just the extreme end of low/reduced carb eating.

Note that people on insulin should take special care in reducing their carb intake as insulin intake will probably need to be reduced to balance things out.
Sally

Hopefully your doctor will have put you on some sort of 'sliding scale' insulin - where the dose you administer varies according to what you blood glucose is. That way you can help minimise the risk of hypos. It might also be worth considering some sort of continuous blood glucose monitor until you have worked out what effects your new diet is having.