I need help with this question pls. It is about the medieval society. Thanks!!?!

Feudalism is built on mutual obligation. In Medieval Europe there was a system in place that despite some minor differences (names etc..) worked in exactly the same fashion regardless of your country, faith etc. You had slaves/serfs men that were not free, the common people, vassals who were free men and land owners, lords and monarchs.
Obligation runs through every single stage and often is linked to mutual gain and protection. Of course obligation was also linked to the law of the land and fear, which was used arbitrarily during this period.
Slaves were obligated to work for free as their masters had paid for them and the law supported this. The average commoner was obligated to pay taxes in return for the protection of the city guard who prevented lawlessness from prevailing in large cities. Vassals are obligated to Lords if they wanted to remain in control of their lands. The obligation often came in the form of tax. Lords were obligated to their Monarch in order to maintain their position and influence in court. They were also obligated to take up arms to protect the Monarch and his lands, by law and tradition.
As you can see obligation ran throughout medieval society and was in fact the crutch that allowed the society to flourish and eventually develop in to more modern versions of governance. Obligation is still found in modern culture in the form of tax. We are obligated to pay tax in order to use the governments roads etc.