@Animelover4ever you can copy the link to a video or photo and before you publish your story, you can paste the link of the photo/picture there :) To find where to paste the link, just click 'advance' in the options box :)
Oh, if you want to upload a picture from your computer to your story, just click the chapter you want the picture on. On the side above your cover for your story, you just press the 'photo' button :)
Hopes this helps ^^