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 to prepare your muscles for the physical effort, you'll run 2 x 10 minutes and walk for 3 minutes to recover between the 2 repetitions.
You will finish with 5 minutes of slow walking to help your recovery, and thereby reduce any stiffness.
Good luck