Click on the little pic that shows a mountain (hovering shows insert /edit image). In the pop-up choose Browse. Navigate to wherever on your computer / device the image is stored. Choose it and click open. Then you get a chance to choose size - I would suggest medium. Then click Insert Image. If you want to copy from another site - like a hosting site - click From another site under Browse - you will then need to insert the image tag - copy and paste. In this case leave it at Full Size. Click Insert Image. Then click Post. If you get some message like "This message cannot be pasted because it in includes HTML" just ignore it and click Post again. You always get a chance to preview before you post. If you are accessing eBay through a device and eBay app, you may need to navigate to the bottom of the screen and choose Classic Site.
Is your vase like the "Shell Panels" shown here?
http://estatesalestore.com/gallery2/main.php?g2_itemId=151585
There were once (like 5 years ago) several Crown Crystal collectors here but like most others they have gone. Many originally went to the eBay Collectors Facebook page - they may still be there and may be able to answer you question. But posting an image here would help.
