Media Bin is used for the CURRENT PROJECT that you have opened. The Library that will be discussed next is used for ALL PROJECTS. Besides importing and using media in the Media Bin, you can do the following:
Use views to sort and find media.
Right-click to Select Unused Media that has not been used on the Timeline and then right-click again to Delete Unused Media from Media Bin.
Right-click on a media to choose Select on Timeline or right-click on media in Timeline and choose Select in Media Bin.
There are several ways to import media into the Media Bin:
Double-click on a blank area in the Media Bin (preferred). NOTE: This method is like After Effects.
Select File > Import > Media.
Press CMD/CTRL + I.
Press the B key and then click the Import Media button.
Right-click inside the Media Bin and select Import Media.