After clicking the upload button, you will see the below popup.  Upload a photo from your computer.  If you are unable to upload a photo, check to see that the size and file extension corresponds to whatever restrictions are given here.  If a photo is too large, or is of an excluded format, then you will be unable to upload the photo.

After clicking the upload button in the lower lefthand corner, the photo will be uploaded in your directory.  You can then click the photo, once, and it will be inserted into a popup.  Clicking "Insert" will then insert the graphic into your webpage.

Although not explained in this tutorial, there are several other functions which you can make use of.  For example, clicking the "X" icon above will delete the photo permanently.  Clicking the hammer icon will allow you to do simple editing, such as resizing or cropping.  However, if you have access to Photoshop or other image editing program, it will probably be easier to edit your photo there.