Question

we are able to walk due to what force

Answer 1

First I want to point out that when you are walking, when  foot is on the ground, it  does not move.   That means that the sum of the horizontal forces on it are zero.   The muscle in your leg is pushing the foot backwards.   We know this because if there was no friction, your foot would move backwards.    So the compensating frictional force must be forward.

Answer 2

Its the frictional force. When you walk your feet push the ground backwards and according to Newton's third law, the ground pushes you forward. The ability to overcome the gravitational force and atmospheric force which requires energy.