Welcome back to the wonderful world of Amigas.
Hopefully you have an Install disk. Fire that up, and load HDToolbox to partition the drive. Once the partitions are ready, use the Format utility in Workbench:System to initialize them. Then use that same disk to install Workbench, and you're good to go.
If the Install disk isn't bootable, boot from Workbench3.0, and then use the Install disk. I don't recall how it's set up.