Start small!
Before every run, do a quick dynamic warm up routine to get those legs loose. Think lunges, squats, hip circles, leg swings, and butt kicks. After a few minutes, start running at a comfortable pace and alternate with walking segments.
Over time, the walking portions will decrease and you’ll be running nonstop. As you’re just getting started, run no more than three times per week. After a few months you’ll start to taste that runner’s’ high and can begin increasing your mileage each week!