After you upload your image file, it will give you a link to it. (right click to copy the link)
Use that link to post your picture. I modified your tutorial to give you an example with your image.
btw can I used images that are not mine for tutorial purposed i.e from wikipedia
Wikipedia images are public and you can use them, but say something like this under the image:
"image credit: Wikipedia.com"
To use other images that aren't yours, you need to email the author and ask. Remember to always credit them or otherwise it is plagiarism.