Before we begin please note that you can not make uploaded files (pdf, word docs, images, etc) private, ever.
Even if you place an uploaded file on a "private" page the file itself is not private.
If you upload any file to the site it will be viewable by the public and may be found by search engines such as google. Never upload any confidential file to the website.
Click "edit" on the page you want to add a file to. Once on the edit screen, click the "Files and Video" tab.
Use the "Files and Video" tab. Click "Choose File" or "Browse" (the language changes between Mac and Windows). Locate the file on your computer, click "Open" and then click the "Upload" button.
Your file should now display in the list of files, which is directly above the "Add a new file" field. If you wish, you can add a description to your files. We recommend unchecking the "Display" box. If you don't uncheck the box, these files will display and sit at the bottom of your page.
You can fill out the "Description" box if you'd like.
You can have the text of your web page link to the file. Do this by right clicking on the file name and opening it into a new tab (pictured below). Go to that tab and copy the web address. Then embed a link with the address of the file.
If you opt to display your files and you want to change the order they display in, make your way back to the "Files and Video" tab of the edit screen. Once there, use the quad-arrow cross to the left of the file name to drag and drop the files into a new order. Click the "Save" button, and you should see your files displayed in the proper order at the bottom of your page/content.
Sit back and admire your work, you file-adding maven.