High intensity interval training (HIIT) is a common method of conditioning and training. The concept is pretty straightforward. Work hard for a short period of time, rest for a moderate period of time and repeat. Because the rest and work ratios are set up in a way that doesn’t crush you on any given “set” the benefit of HIIT is that you can actually accumulate a fairly large volume of high intensity work over a short period of time. It is kind of like using cluster sets, but for conditioning.
One of the biggest mistakes people make when performing HIIT is that they don’t appreciate how to actually structure the workouts. They think that HIIT means crushing yourself at all costs at all times. But this is not the case at all. Instead, it's actually much more about a methodical progression from short bursts of workouts with long rest ratios, to slightly longer bursts with shorter training.
You can start with a work to rest ratio of approximately 1:4 and work your way up to 1:1. What does this mean? Well, you could start by doing 15 seconds of high intensity work (burpees, sprints, sled pushes, etc) followed by 1 minute of rest, repeated for 10-15 rounds. You would simply ramp up the amount of work and decrease the amount of rest slowly over time. You would eventually work your way up to 30 seconds of high intensity work followed by 30 seconds of rest, repeated for 15-20 rounds.
Just make progress methodically just like with any other type of workout, and you’ll likely see some great results with fat loss (in conjunction with a caloric deficit of course) and your overall conditioning.