To convert them back to text just drag and drop them onto a text based app window.
Text clippings are a bit of an oddity - something of a hold over from the Mac OS of yesteryear.
You might prefer to use the Services menus options to send text to a Sticky or TextEdit. If you have OmniOutliner installed (which, if you have a new Mac will be), it has a Clippings feature (it will create a time stamped database of clippings you send to it)... might be an OmniOutliner Pro feature though:
Note, unfortunately, Services don't work in all apps. Also note, you can assign your own keyboard shortcuts to menu items in the Services menu, just ensure that they don't conflict with any used in your apps, by the OS or by other Services. You can also control the content of the Services menu using a freeware app called
Service Scrubber