Here is an article on managing files.

You can actually upload files from this page and then get their URL for later use.

If you create some simple text and click the link button in the WYSIWYG you will then be permitted to upload a file and that uploaded file will have a URL associated with it.

For instance, here is a link to your logo:

The URL to this file is the following:

Created by Jenn:

Created by Jenn: