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 30 seconds of running and 30 seconds of fitness walking, for a total of 10 minutes.
After a 3-minute recovery walk, you will start the 2nd repetition of the exercise.
The session will finish with 5 minutes of slow walking to help your recovery, and thereby reduce any stiffness.
Good luck!