When your blood glucose and insulin levels come down and your body runs out of readily available stored glucose in your body for fuel, your liver will start creating ketones from stored body fat to use as fuel.
This is called “ketosis,” and it’s the basis of the Ketogenic diet.
This process is what people are referring to when they say “fat burning,” and it’s the metabolic process that every person trying to lose BODY FAT is trying to achieve.
The really really really simple way to achieve this through diet is to keep carbs very low, especially refined grains and sugars. This lets your insulin levels stabilize and your glucose levels to come down. As your body gets into the habit of doing this, it will be able to achieve ketosis on a more regular basis.
When that happens, your body gets GOOD at burning fat.
If you want to supercharge this, adopt an intermittent fasting schedule, something like a 16/8 (fasting to feeding). This will help you get results faster AND maintain them due to the many benefits of IF like hormone regulation and increased insulin sensitivity.