There are basically three ways of inserting pictures on to a wikidot page.
First, in edit mode, click on the little green icon that says "insert image wizard".
1. External image via URL
2. Attached file
3. Picture from flickr.com
Use 1) or 3) if you want the picture from the internet, and 2) if you want to upload a picture from your computer (such as a private photo).
External image (1) is simple: just paste in the URL address in the space provided. This URL you may get from e.g. Google Images, once you have clicked on the image you want. Then "check it" to see if everything works.
Pictures from flickr.com (3) are also easy. (description will follow)
If you want option number 2 - uploading one of your own pictures - you first need to upload the file. In "article" mode, click on FILES below. Then, upload a file from your computer. Select files, and choose your image. Then, in EDIT mode, click on the green icon again ("insert image wizard") and choose the option attached file. Then, click on the title of the image and choose size and position for your image. It will then be inserted directly onto your page.