When you are starting out or getting back into running, alternating between walking and running will help you build up your endurance to run for longer periods without stopping!
After 10 minutes of fitness walking, which will prepare your muscles for the physical effort, you'll alternate between 1 minute of running and 40 seconds of walking, for a total of 10 repetitions.
You will finish with five minutes of slow walking to help your recovery, and thereby reduce any stiffness.