Fiefs were earned by the peasants when they worked on the lord's manor. Knights were also given fiefs in return for their military work.
The peasants also had to pay a church tax called a tithe, or in other words, the canon law.
A fief was a parcel of land held by a serf. It was given to him by his overlord, and the serf was required to work it and give him a share of his crops every year.
A fief is something real or tangible given for loyalty by a person of higher rank or status to someone to retain loyalty. It was usually a plot of land, and it might be accompanied by a title, rank...
In the expression ''I will answer after I have received the the letter" the speaker is saying that they have not received the letter yet, but when they do, or rather, after they receive it, they will...