Mass is a fundamental property of an object that does not depend on the position or velocity of the object. In other words, for every action there is an equal and opposite reaction. They exist in pairs, act on different object, and never cancel each other. Friction is the retarding force acting against the sliding between two contacting surfaces. The direction of frictional force always acts opposite to the direction of sliding.
Static friction is the maximum force acting against any start of sliding.
When you push a heavy block on the floor, the block will start sliding only if the push force is over the critical value of static friction. Sliding friction is the retarding force during sliding. It slows down the sliding velocity. Sliding friction is a little bit less than static friction. FN m is the coefficient of friction which varies with different surfaces.