To access the file storage area in your account, login to your email account through the web interface, and click on the 'Files' link.
Alternatively, use the DAV or FTP interfaces.
You have a quota on the amount that can be stored in your File Storage area. There is also hourly and daily bandwidth transfer limits. If other people download your files via the web (because you have created a website) then that is still counted towards your transfer. Uploads and downloads via DAV and FTP are also counted.
The size of your bandwidth and storage quotas will depend on your service level .
Using the web interface, the maximum file size you can upload is 50M. If you use DAV or FTP, you can upload files as large as your file storage quota.
The File Storage transfer and storage quotas are completely separate from the quotas on your mailbox, so if you reach your File Storage transfer or storage quota that will not affect your email.