Feudalism was an arrangement in which one nobleman owed allegiance to another. Under this arrangement, a lesser nobleman, commonly called a vassal, swore to fight for the upper nobleman, known as the lord. In exchange for the vassal's pledge, he was given a grant of land by the lord. This arrangement was solemnified in a ceremony known as homage and fealty. Each person who entered into the arrangement was a member of the nobility. The vassal himself might be the lord of another nobleman; and the lord might also be the vassal of still another. At a time when few people outside the clergy could read and write, the obligation was bound by one's solemn oath. His word was his bond.

A manor was normally the land granted to the vassal. Since there were no towns and very few cities, the manor operated as a self contained unit, with its own blacksmith, mills, granery, etc. Even the roads which traversed the property belonged to the vassal. He was, of course, known as the lord of the manor, since the property was his, and all who lived and worked there rented from him--he was literally the "landlord." Rents were paid with a portion of the crops and hours worked on the landlord's personal lands and roads, etc., as money was practically non-existent. Those who lived and worked on the land were serfs. They were little more than slaves who could not leave the land or even marry without the landlord's consent.

So, in a nutshell, feudalism was an arrangment whereby land was granted to a nobleman; manorialism was the system by which the nobleman operated the land granted to him--the manor.  

The difference between these is that the manorial system was one part of feudalism.  Feudalism was a bigger system than the manorial system.

In the manorial system, some lord would be the ruler of the manor.  He would be in control of its economy and even of its law.  The people who lived on the manor would be under his control.

This was the lowest level of the feudal system.  Above the lord of the manor there could well be other lords.  The lord of the manor would owe allegiance to some lord who was above him.  This went up all the way (in theory) to the king of whatever kingdom the manor was in.

The manorial system, then, was an integral part of feudalism, but it was only one part of the feudal system.