Click on the "File Attachments" link in the navigation bar on the left.
You probably want to create a folder for your project. For example, I might want to create a directory called eds. Where it says "Create New Directory in default directory, type the name of the directory you want to create.
Push the create button
(If you already created a directory, you can navigate into that directory by clicking on the folder name in the list of files.)
To upload a file:
Click the browse button and find the file in your local file system
Click the upload button
The file will be added to the current directory.
To access a file
Type the pathname within a pair of * and + characters. For example, if I create a directory called eds and upload a file called eric.pdf I could reference this file by typing