Employees can be classified as teachers or administrative staff. This is specified on the employee's profile in the "Employee Type" field.
Teachers only have access to teaching functions and only have access to records related to their own teaching (ie. Their own lessons, students, etc.).
Staff accounts are for employees that perform administration and need access to non-teaching functions in Teachworks which you can customize in their permissions settings. Staff accounts can also be used for teaching by enabling the "Include as Teacher" option on the employee profile.