The QGIS QgsWcpsClient1 plugin allows sending WCPS queries to a server for display and further processing the results in the client. The steps below describe how to install and use it. And no, don't ask us how the plugin got this weird name!
In the QGIS toolbar open the Plugins menu. A dialog will appear guiding through installation. Type WCPS in the search box to spot the plugin.
Now that the QgsWcpsClient1 plugin is installed a rasdaman icon will appear in the menubar. Click it to open the plugin.
Now we need to create a connection to a server which implements OGC WCPS standard; for our purposes we use this site's endpoint, https://ows.rasdaman.org/rasdaman/ows. With New open a dialog, type in some server name, say rasdaman ows, and the URL of the server endpoint. With an Ok this new connection gets added to the list of known servers.
Select the dropdown menu of available server connections and then the rasdaman ows element (your newly added server connection). Then, click the Connect to Server button to connect to this server endpoint.
Now QGIS is ready for work.
In the ProcessCoverage tab,
type the WCPS query into the Queries text box.
Note: For QGIS, the query must return a 2D image.
And we're done - via the ... button select a local folder path to store the image result.
Finally, click the ProcessCoverage button and the image result will show in QGIS's main panel. Bingo!