OK, I'll bite. You're going to interview for a job and you don't know what's involved?
UNIX Administration
Install, configure, and sustain computing systems running UNIX (or UNIX like) operating systems.
Perform / manage routine system backups, system monitoring, account creation and account deletion. Gather and/or write scripts to collect performance metrics, monitor disk space, i/o usesage, cpu useage, abnormal system use, detect intrustions, and/or other security vulnerabilities.
Design, develop, implement and/or Specify standardized procedures and scripts for doing one or all of the above.
Server and/or Workstation harware support. Replace failed power supplies, disk, processors, or main boards.
Depending on the environment UNIX Administration might also include any or all of the above for specific applications and/or database products. Network administration and even PC / desktop support are a possibility. Help desk and/or a customer call center could also be a duty of a UNIX admin.
Good luck.