Well, my dad is a little overweight and has arthritis in his knees but he told me that walking 2+ miles a day has helped his mood. He even gets my mom to go on a walk with him sometimes! He told me his knees aren't hurting as much.

The best way to start doing *anything* is small. Walk for 10 minutes. Then 2 days later 15. Slowly work up to a consistent time, and walk/bike fast enough that you can feel your heart pumping. You won't get fast results this way, but it is actually the safest and easiest way to start a routine.

Also, if you are going to walk, it's a smart idea to have a couple different routes otherwise things get boring fast. (or drive to the park and do it. idk, be creative)