Warm-up: Light stretching. Spend 5 minutes stretching your hamstrings and quads. Here is a 5 minute stretching video. Only do what you are comfortable with. https://www.youtube.com/watch?v=-iY5V0xiiKw
WOD: 20 minute cardio. Walk outside or on treadmill, elliptical or bike (recumbent, upright or AirDyne). Easy pace. Do it in bunker gear, no airpack. This is a starting point. Commit to doing this workout 4 to 5 times a week.