Uploading and linking to files on such as PDFs on your website is a two step process. The first step is to upload the file to the repository using the upload screen under the SiteMaker "Site Editor" tab.
Using the file selector on this screen, upload your files, and provide names in the fields as needed. You can upload multiple files at once by selecting multiple files from the dialog while holding the ctrl or command button while you click (depending on mac/pc). Flash is required to be enabled to use the file uploader.
Now that you have uploaded and named your files, click on the Sitemap icon to return to your list of pages. Click on the page which you would like the file to appear as a downloadable link. Then choose the section you'd like the link in. This must be a "General Content" section type which includes the text editor.
On the text editor you will find an icon that looks like a chain link. This is the insert link button. Highlight your text in the text editor and click that link to hyperlink the text.
When you click he insert link icon, you will be shown an "Insert Link" dialog box. Use the drop list for "Link List" to select your file (you can also select pages on your site to create contextual navigation), and click the "Ok" button.
Your text should now be linked. Save the page and you are done. You have created a link to an uploaded file on your website.