Use the navigation hierarchy on the left to browse to the appropriate section. Note that these sections are actually pages that have Child pages.

Click on "Add" in the upper right of the screen and select "Add Page"

Enter the Title of your page in the "New Page" field at the top.

Use the WYSIWYG tool underneath the New Page field to enter text. The WYSIWYG works much like a scaled-down version of Word.  You are encouraged to use Heading styles (see the Paragraph pull-down menu) as appropriate as they are useful for creating a Table of Contents.

We also recommend using the Table tool to assist with positioning images, just as you see with this document. Click on the tool and wait for the pop-up dialog box.

We recommend starting with a 2-column, 1-row layout with the "First Row is Heading" box deselected. Just as with Word, you can use the Tab button to create new rows as needed.

If you are not comfortable using Photoshop to annotate and resize images, PowerPoint is a useful alternative.
Create a new presentation and delete any text box other other placeholders.   
Insert an image then resize so it fills the scren using the handles per the image at right.
Use PowerPoint's drawing tools to add any arrows, circles, or notes as desired.
Repeat as needed for every image needed for a specific Wiki page.

When you are finished with all the slides, click the "File" tab then click in "Save As"

Select "JPEG FILE Interchange Format" from the "Save as type" pull-down menu.

Export Every Slide.

The confirmation dialog box will show you folder location containing all the jpgs.

Once your images are ready you can upload them using the image upload button in the WYSIWYG Toolbar

This brings up the Insert Image dialog box.

Click the Browse button and locate your image, click Open. This will return you to the Insert Image dialog box.

Note the two checkboxes at the bottom of the dialog box. If your image is large, click on the "thumbnail" checkbox to upload a small version image that the wiki software creates for you and automatically links to the larger version. The other checkbox puts a thin black border around the edge of the image.
Click "Insert" to upload the image to the page.