Yes, the image (at the end of that link you posted) is where you would select your image. You need to put it into your project first though.
So steps to do:
- Drag the image (hopefully it's in PNG format?) into the sidebar in the left and tick the checkbox titled "Copy items if needed" and click finish. Now you should see the image in your project.
- Go to that place in interface builder that you have in the link (here: http://prntscr.com/5x7gn0) and select the image you added from the drop down list.
There is another way you can do this; programmatically, but it's slightly trickier. You still do step 1 but then instead of step 2, you can create an outlet to the Bar Button item and set its image like this:
barButtonItem.image = UIImage(named: "imageName.PNG")
If you need any clarification of what I've said, feel free to ask.
Loic