Having formated the drive, you don't have an operating system (OS). So commands such as SETUP won't work.
With older OS you would have had to copy the basic operating system to the HDD and then install a CD driver. You could then have inserted the CD, changed to the CD drive and run SETUP.
Thankfully, XP will install straight from the CD drive without having to go through all that - assuming that your PC supports booting from the CD.
Reboot your PC and go into the BIOS (normally done by hitting the DEL key as it starts booting.)
One of the menu selections will be Boot Order and will give a variety of options such as Floppy, HDD, CD - HDD, Floppy, CD etc. Select one with CD as the first choice. Save and exit.
Insert the XP CD in the drive and reboot. Follow the XP prompts from the screen.
If that doesn't work, you'll need to download a set of 6 XP boot floppies from Microsoft on another machine. They can be found
here for XP Home and Pro, both for the original XP CDs and the later Service Pack 1 (SP1) editions.