helper or Library

[eluser]jaswinder_rana[/eluser]
I want to have the functionality of creating directories.

Now, I am not sure if it should be library or helper.

What I am trying to understand is,

- When to use helper?
- When to use library?

In CodeIgniter's context, I am trying to understand the main difference between these two.

Above is just an example. As I am new to CI, I am trying to understand the mindset when this framework was written so that I can proceed as needed (expected?).

Thanks