I believe you load your pics into your computer and name the file when complete. When you open the thread there are some icons at the top for font sizes, then bold, italic, and underline, then font and size etc.... keep going to the right and one of those icons says image. Click that icon, then click from computer, then select files, pick your picture from the computer then upload.
I'm no expert so hopefully if this is wrong someone else can give better advice.