You have to start at Level 1.
If you have a PERC or SmartArray or what ever HBA you own you need to create a "Virtual Disk" with a Raid first. Even if you only have a single disk you need to create a RAID0 in such setups.
Otherwise tell us more about your HW setup.
Level 2:
Perform a HBA rescan on ESXi and than create a VMFS Datastore on the new detected device.
Regards,
Joerg