this the century's biggest misconception.
from defn.'friction opposes motion or tendency of relative motion.' mostly friction acts oppo. to direction of motion,but not always. check the direction in which there is tendency of motion.that solely determines the direction of friction.
for example,when a car moves,friction on rear wheel acts in direction of motion of car while in front wheel friction acts opposite to direction motion of car
						

							
Hi
It depends upon the situation. It always acts against the relative motion. Eg, while walking the friction helps us to move forward. the friction force is in the direction of our movement. We push our foot against the floor and in turn to avoid the relative motion n friction pushes us forward.
But while sliding friction acts against the motion. Therefore it all depends upon the situation. So, finally everything boils down to relative motion.
						

							
Hi,
NO,friction does not apply in the opp. to the motion in all the cases.for ex. suppose two blocks are placed on each other and we exert some force on one block then friction will oppose it but this friction will support to the second block to move with one block.second ex. can be of riding of a bicycle.