Manors
Vassals were loyal to the person(s) above them. Therefore a king may have a vassal who may have other vassals loyal to him. A vassal has power over his serfs, or his vassals. Also the vassals have power over the peasents.
the vassals would give protection to the serfs and also protect the land
The vassals required to give their king land. They could also give the king food, water and a sword.
The plural of vassal is vassals. As in "our vassals have sent us gifts of silk".
Vassals had to serve lords because the vassals promised to serve a lord in exchange for land.
In many cases, vassals did have their own vassals, in a process called subinfeudation. There is a link below, but it does not give as much information as I would have liked to find.
The dressing of the vassals was a tunic that had covered their leggings.
Vassals could receive more land from the lord and if they were rich enough, vassals could become a lord to other vassals. Feudalism could become confusing.
Explain the difference between the vassals and the serfs
Yes, vassals can have children. Their children may inherit their titles and lands, continuing the family's lineage and influence within the feudal system.
A Medieval Lord was simply known as LORD, YOUR LIEGE, or YOUR HONOR. The rank below a Lord was vassals, below vassals were serfs, which is the lowest position. Also he could be known as Sire.
Lords granted lands to vassals because they had a lot of land and needed men to fight in their armies. They also couldn't manage their land alone. As a solution, a lord would give land to vassals in exchange for the vassals agreeing to fight in his army. The vassals would have peasants and serfs work their land.