Since you exert your weight (the force with which the Earth pulls you downwards) on the ground, the ground exerts another force (normal force) on you. In case you are not accelerating upward (vertically 0 acceleration), the normal force equals you weight (in magnitude). But since both of them are opposite in direction, they cancel each other. So, the net force vertically is zero.
Now, the normal force is one of the reaction forces. Now, coming to friction, your thought that friction always opposes motion is a misconception. When a car accelerates on a road, what helps the car to accelerate on the road is friction.
Now, coming to walking on a road, what you do is push the ground backward with your feet to help you move forward. So, here the ground tries to oppose the force exerted by your feet by applying a frictional force in the opposite direction.
But, since the net horizontal force "acting on you" (that is frictional force) is in the forward direction (that is your direction of motion or the direction in which you want to move), you are able to move forward.
Now, the reaction forces (talking individually) are two and both are vectors. One is the normal force (which is always perpendicular to the surface, and the other is the frictional force. So, the vector sum of the two is called the "contact force".This is the one basically that you consider as the "reaction force".