What your tutor needs you do do is change from reading from a file - your
Stream - to reading the data directly from the user.
To do that, you need to get rid of the line:
using (Stream input = File.OpenRead(filePath))
And replace all references in your code to
with references to the
class, and use the various Read methods (Read and / or ReadLine) to fetch the bytes from the user.
You will need to decide how the user enters the bytes (he can't just type them as he would be restricted to just the characters available from the keyboard while byte values range from 0 to 255) then decide how you tells you there are no more and so forth.
Sit down and think about the task, and what you learned in the last lesson - it should be pretty simple if you paid attention!