There are 2 options to add media from Google Drive to a video editing project in Clipchamp.
Use the direct file importing feature in the Your media tab. When you select the down arrow next to the Import media button, Google Drive will appear as one of the options you can choose.
You'll get asked to log in to your Google account. If you have more than one account, make sure you select the one that is linked to your GDrive files.
After you have linked your Google Drive, a window will appear that shows the contents of the drive. Select the media files you would like to add to Clipchamp, then click on the Select button.
Download the files from Google Drive to your computer and then add them to your project from your local drive.
If you're on a Chromebook, the steps are very similar and described in the following article: Using Clipchamp on a Chromebook.