A website can contain a lot more than just text. You might want to upload images and provide links to existing documents.
If you have a newsletter in PDF format for example it is a lot easier to upload the PDF to the website and give visitors a link to download it, rather than typing out the same information on the website.
Similarly if you have Word documents or Excel files that require input from visitors/members it is often easier to upload those files to the website and provide download links.
Images, Documents, PDFs, Spreadsheets etc. are all assets, and are created using the 'New' button.
