You are allowed to have ONE image (a banner) in the SUMMARY of your story . (And also chapter banners, from what I know; one per chapter - which I didn't think was all right, but I think it was Dujo who said it was okay a while back.) If you're trying to put pictures of your characters up, use the characters option you already have. (My Mibba > Stories > Characters.) You are not allowed to have links in the chapter content of your stories; they are only allowed in your long summary, and author's notes.
If it's saved onto your computer, you would go to an uploading site like Imageshack and upload it there. Then find the thing that says Direct Link and copy it, and then you use that link in between the [img][/img] tags. :3
are you asking how to link pictures in it? or how to put an actual image in there? to put a link, you do this: [url=the link]link title[/url] and for an image you do this: [img]the image link here[/img]