Talk to others you know as likely someone you know wants to start a fitness routine. Having someone to help motivate you makes the process of starting and sticking with it a lot easier. Good luck you can do it!

What are the best exercises that burn the most calories in a short amount of time?

First of all, do what you like and don't overthink it. You don't need to do crossfit or hours of cardio to be functionally fit and healthy. We know maintaining an ideal weight is mostly diet. Sure, calories in calories out, but it's too easy to out-eat any exercise regimen.

Just 20-30 minutes of getting your heart rate daily up is fine. Of course if you have aesthetic goals in mind that's another story. As previous posters have said, a buddy is good motivation.