The large muscles of your thighs are designed to be your natural shock absorbers as you walk and run. Using them more can help reduce injuries and increase endurance.
Most of us heel strike as we step. This means we put our heel down first with each step. All your weight plus the impact of striking a small area transfers a tremendous force up your leg to your body.
To take better advantage of your thigh muscles, place more of your weight on more of your foot as you step. As you shift your weight to your foot keep your knee slightly bent. The force of walking or running is spread and absorbed by your legs.
This takes practice. Begin by lifting one foot off the floor and holding/dangling it in front of you. Carefully shift your weight forward and place this foot down with your weight more to the center of your foot than on your heel. Go very slowly so you have complete control of how you place your foot. Keep going one slow step after another. With practice this becomes easier and you can progress from this very slow walk to a normal walk and, eventually, running.