The sons of noble families were educated and trained as warriors. Were pages and then squires other gentlemen first.
At eighteen years were named knights in the investiture ceremony in which they received their weapons: sword, shield and chainmail. From that moment, would be part of knighthood and should be courageous, loyal to his master and defend the weak and women.
The nobles waged war to defend their territory or ortho help the monarch or lord who owed allegiance. The war provided, if won, land and wealth which enhanced the power of the nobility (booty).
Their social function allowed the nobility live with privileges. They had to work, did not pay taxes and were the only ones who could give them weapons and exercise control over the rest of the population.
Women, although they were of noble family, were subject to men, either the father or husband. They could inherit, and in the absence of men, to be holders of fiefs, but usually their marriage was acting in concert with nobles and their lands passed into the property the husband's family.