You can import media files into your project either by using the Import dialog box or by dragging. If the Interpret Footage dialog box appears after you import a footage item, it contains an unlabeled alpha channel, and you must select an alpha channel interpretation method or click Guess to let After Effects determine how to interpret the alpha channel.
Imported footage items appear in the Project panel.
Import footage items using the Import dialog box
Import footage items by dragging
If you always want
the layered footage that you drag into After Effects to be imported
as a composition, choose Edit > Preferences > Import (Windows)
or After Effects > Preferences > Import (Mac OS), and choose
Comp from the Default Drag Import As menu.