importing stills/video from memory card to iMoive

I have started a project in iMovie and have gotten some stills/video into the project, but I have some other stills/video on a memory card which I want to import.

How do I import those stills/video into the project? When I click on iMovie's file>import after highlighting the memory card shown on the sidebar, I get an iMovie error message which reads, "Folder is not a movie archive. Please select a folder that is a camera archive, then click import".

What do I do to get the material on the memory card into the project?

Thanks for your help.