Hello~

First, after you've finished your picture you need to upload it to an online image host, like dropbox or mediafire or postimage.org, or whatever one you like.

Then when you click Create New>Picture in the sidebar to the left of this site, there'll be a little box that says something like "Paste image url between [img] and [ / img] "

Go back to where you uploaded your picture and copy the image's link, make sure the link ends in whatever file type you saved the picture as, normally a .jpg or .png

paste that link between the [img] tags in that box

and you're done! :U

Thanks