When two surfaces rubbing against each other some resistance is produced. This resistance is actually friction force. It acts to stop the movement of two touching things. You can say that friction is a loss in the form of heat and sound. There are several types of friction like dry friction, fluid friction, skin friction and internal friction.
Friction has number of applications in many engineering disciplines. For example:
Automobile Brakes depends upon friction.
Ignition of matchsticks.
Writing with a pen.
Placing anything on a surface depends upon the friction due to their roughness.
Check out these Videos how Friction is helping for Welding: