You should aim to walk for 15 minutes every day. Not ambling, not sauntering whilst chatting with your friend, I mean proper walking: striding out, using your joints and muscles to the best of your ability. Walk as fast as you can without breaking into a jog (as if you might be tempted!) but do concentrate on where you are walking - keep a keen eye out for tree roots, uneven pavements etc. Walk early in the morning if you can. There will be less people around (important in covid-19 times), the sunlight is better (you may not need to wear sunscreen if it's before there is much heat in the sun) and you can tick off your vitamin D uptake for the day. Try walking with one earphone in listening to a talking book (or podcast or talk radio) - but I don't recommend using both earphones else you might miss that electric car sidling up to you as you are about to cross the road. Happy walking!