Sounds like you're interested in free running/parkour with a question like that. If you don't have access to a gymnastics gym. Start outside on a soft surface like grass and practice front handsprings, you shouldn't get too hurt from doing those then slowly start to learn a front flip. It's all about slow progression don't go outside and just try to do one you will get hurt.

The way I did it is on a trampoline, start with a simple roly poly and then gradually build the height, bouncing on your knees then roly polying, then jumping, then take time to heighten it and within a few days/weeks I was able to do a flip, you need a lot of time to perfect it on ground though :-)

Start on trampolines. Try doing a forwards cartwheel/hand spring. You could go to Extreme Air park ans start there. Once you are more confident. Try holding your hands a little higher so they don't touch the trampoline/ ground. Then you can work on tucking in and doing it on solid ground.

Preparation.

The best way would be private lessons with a tumbling coach.

wing it