A noble can be both a lord and a vassal, since they are the monarch or queen's vassal, yet they are a lord to their knights. He established feudalism in England to compensate his knights for their devotion. A noble could not fight wars or lead armies himself, but he could grant land to others who could do these things for him.
Feudal service was required of anyone who wanted to hold land in France or England. They would have to serve the king for some years at his command. If they were young and strong they might be given a small piece of land of their own. Otherwise, they would have to return home.
In medieval Europe, many people were still working the land themselves instead of renting it out. The nobility took care of government business (which included warring if the king asked them to) while most men worked on their farms or served in the army. It was common for there to be more soldiers than farmers in some countries.
The nobility had the advantage over everyone else of being trained from birth to fight on horseback. This was very important when fighting other nobles or kings! They also tended to live longer than other people. All in all, it was easier for someone from a rich family to find work as a knight or soldier than it was as a farmer.
Nobles can be lords as well as vassals. Feudal land rights were typically awarded to the nobles. If a noble (noble 1) enjoys feudal rights on a huge property (land A), for example, and grants feudal rights on a smaller portion of this land (land A1) to another noble (noble 2), the latter becomes his vassal. If the relationship breaks down, the original noble has the right to take back his land.
In modern Europe, many countries have noble titles. However, in most cases, these are non-feudal titles that were not derived from land ownership but rather from some official position such as minister or judge. France has several million people with noble titles. In fact, it is the largest country in Europe with a royal family. However, only about 300 families out of the millions living within its borders are actually noble. They hold their titles because of some relation to the monarchy, but they do not own any lands or castles. On the other hand, Germany has very few nobiles. Only around 70,000 people out of its 900 million population are titled because they come from ancient Germanic clans. Again, they don't own any land apart from small plots given to them by the government.
In Asia, many countries have noble titles. But in most cases, these are also not based on land ownership but rather on some official position such as governor or mayor. India has many millions of people with noble titles.
All named nobles are lords as well as vassals. So, every member of the titled aristocracy (barons, counts or earls, dukes, and so on) is a vassal of the monarch. Because they would have all had knights, the nobles are lords of the knights, who are vassals of the nobles. Thus everyone in the nobility is someone you should try to keep happy.
They also have authority over other people who are not part of the nobility but still enjoy protection from them. These include: priests, ministers of state, mayors, governors, military commanders, police chiefs, and other administrators.
In modern countries, the nobility usually consists of old families that were rich enough to be able to buy titles. In some countries there are laws against inheriting titles because it can lead to many problems including conflicts of interest for the new owner. In these cases, the titles must be granted by the king or queen. However, many titles are held without being inherited because most owners do not want to burden their children with such responsibilities.
Overall, nobles are people who can afford to pay for services rendered by others. They give orders to lower-ranking officers and soldiers, administer justice, conduct government business, and otherwise play important roles within their kingdoms/states.