Why don't working this program?

folder =MyFolder
FileName =MyFile

if fs.exists(folder/FileName) then
print("Worked!")
else
print("Not worked! :(/>")
end

1. You have to use strings (MyFolder refers to a variable, "MyFolder" is a string).
2. Strings or nil variables can't be divided (a/b is division)
3. Strings can be combined ("Hello" .. "World" -> "HelloWorld")*
4. However, in this case it's probably better to use fs.combine.

*Note that -> is not actual code, this is just to indicate the result of combining the two strings.