Problem erasing/reformatting mac El Capitan

Attempting to erase and reformat brand new My Passport 4.0TB external drive with older mac (El Capitan 10.11). Opened up Disk Utility but no “Erase” option showed up. Figured the external drive was somehow already reformatted for mac, but I don’t think this is the case. Now the new external drive shows as “Untitled” in left column.

Help please. How do I get my drive erased and reformatted when no erase option comes up?

And now it shows as “Not readable by your computer” when I try to plug it back into my mac’s usb port. Ugh.