Im just going to go right to the instructions for this one
1. find the image you want on the internet
2. right click and choose "copy image location" (not copy link location!)
3. in your post type in [img]
4. hit paste (ctrl-v) and it will paste the image location that we copied earlier.
5. at the end of that type in [/img] (be sure to add the /)
and viola