To use Virtual Observatory, in an existing or new library click the last button of the row of 4 in the toolbar. In the view that appears, select the archives you want to search at the top, adjust the search radius if necessary, and enter the object's name or coordinates. It will then show up a small list of possible candidates with their RA/Dec coordinates. Click the SIMBAD and NED buttons to use these services if your object is not listed. Then click the Search button.
Observatory will search the selected archives in parallel, and you can select or deselect them to extend or reduce the search. You can filter the search results using the search field at the bottom. Expand the Preview section in the Sidebar to see a thumbnail for any selection. Not all archives provide thumbnails. If you move your mouse cursor over the Preview area, you will see a Quick Look icon appear, which when clicked will display the full preview of the image. To download images, select them and click the Download button. If you have an album selected in the Sidebar and the "Add to Album" checkbox on, they will be downloaded in that album. Otherwise they will be downloaded to the Inbox.
A handy feature of Virtual Observatory is that if you have a plate solved image, by selecting it and holding the Option key while selecting the Virtual Observatory toolbar button, it will search the archives right away with the center coordinates of your image. A fast way to find matching images. I think that is what you are referring to in your question. Press the Option key.
Please see the article "Using the Virtual Observatory" in the user manual (menu Help > Observatory Help) for more details.