creating a eDrive

My main hard drive ( Macintosh HD ) has insufficient space to create an eDrive .

Can I use another another drive ( USB ) that has a Mac OS ?

I have a USB that has Yosemite Mac OS and another USB that has Snow Leopard Mac OS .

And of course I can sign into those drives .

( i should note that at this time I have given up on trying to make of use Protogo created by TTTro 11 )

I am adding a screen shot of my desktop/hardrive/USB drives which may help or may not . Hope the screen shot gets picked up .