Can someone explain What is the meaning of Resource Buffer and how to calculate it?

The buffer is the additional time that you add to your project schedule in order to face unpredictable action that can make your calculation wrong. Suppose that you estimate that your project will take 5 months in order to make it happen with unknown risk you can add one week to the 5 months so if something disturb your schedule you can use the 7 days buffer to overcome it. I don't think there are a special unique formula to calculate the buffer it depends on the project manager experience and he can be helped by his team to choose an appropriate buffer. But sometimes he can add an amount percentage of the schedule as buffer such as 10% or 15% of the total time estimated for the project depending on the risk associated to the project.

Schedule buffer and ressource buffer are different.
The explaination for the schedule is good and can be apply in a similar way to you ressources.
A small supplement to you ressource planning.
There is no fit all calculation, experience and field of the project will influence.

There's project buffer, feeding buffer and resource buffer. Often the duration of the project buffer is 50% of the contingency that's removed from each estimated task.

Schedule buffer and ressource buffer are different.
The explaination for the schedule is good and can be apply in a similar way to you ressources.
A small supplement to you ressource planning.
There is no fit all calculation, experience and field of the project will influence.