Adding an image or file to your site is easy with the WYSIWYG editor. Both work almost exactly the same, as it is controlled by the same module.
Adding an image
First, click on the icon that looks like a little tree.
This will pop up a window (see below). Click on the icon that looks like a file directory.
This will pop up another window where you can upload files.
You can browse and upload additional files, or you can select a file that has already been uploaded.
If you'd like to organize your files into folders, you can create the folders via FTP and then use the drop down box under the file listing to select which folder you want to work with.
You can select the image you want either by clicking on add to the right of its name or clicking on the image's name and then clicking on the image when it pops up in that blank area in the box above.
You'll then be taken back to the first pop up window.
You have to input an image description. It's good to input a good, short description since Google and other search engines do pay attention to those.
If you want to align the image to the left/right or anything like that, click on the Appearance tab.
Once you're finished, hit Insert and the image will be added to your page.
Adding a file
Adding a file works almost exactly like adding an image, except you'll need to highlight the text to be linked first, and then click on the button that looks like a link in a chain.
The rest works pretty much the same way - a window will pop up. Click on the directory button.
Browse and upload your file.
Click add to the right of the file's name to add it to your page.
You'll be taken back to the first pop up window. Here you can either hit Insert to finishing adding the link, or use advanced options like forcing the link to open in a new window (helpful if you're linking to a page outside of your own site).