Why can't I drag video from my sd card in file explorer onto a project?? Also If I had started a project with files from a sd card, copied those to a external hard drive and deleted the clips that were on the sd card would the video project say the files are missing? If so could I just find them and tell it they are on my hard drive?
You need to have your media files on your computer's hard drive in order to import them into your project.
Move your video files to your hard drive first, then you can use Add Media/From Files and Folders to locate the files and import them into your project.
Part 2 of my free 8 part Basic Training tutorials shows you how to add media to your project.