Launch the editor for the page in question by clicking on “edit this page”
Note the row of icons for editor actions just above the editor area, click on the one that looks like a picture frame about 2/3rds of the way to the right. This will open a window showing available media files.
Select the namespace where you saved the image above, then select the image.
You can edit the options here or just leave default, then click “Insert”.
The inserted text is the code that refers to the image and inserts it. The text can be copied and pasted elsewhere in the editor to change its position. Options can be edited directly in the code as well.
Preview your changes to the page and save them, just as you would if you were only editing text.