ok...plug in your Hard Drive, dont rename it just plug it in...then go to disk utility, then on the right of the screen all of your Hard drives will show up. select the disk that is your external, not by its name, but where it says the size, then the brand, followed by some other numbers and such. Then above that you have a few menus you can go to, First Aid, Erase, Partition, Raid, and Restore.
Go to Partition. Type in the name you want, then for format i use Mac OS Extended (Journaled) or something of the sort. then click partition and your ready to roll!