To understand the problem, we need to know what FIND does. It returns the location number of the first character in the FIND. If it does not find the value, it returns an error, hence the need to verify that it returns a number (with ISNUMBER).

Therefore, the formula says that if we have FIND return a number (meaning it found the value) then tell me you found it, if not, tell me you didn't find it.

Clearer, now?

Bruce