The device that you received from the company must be either new and unused or have been restored to factory default settings.
For supervised devices, the company will determine which setup steps you have to carry out. It is therefore possible that some of the regular setup steps normally carried out for iOS devices will be masked out by your firm. Follow the setup steps on the device, as described on the Apple help pages.
During the configuration, you will receive a message that the device will be configured by your firm automatically (left illus.). You only need to enter your access data (company email address and your domain password) (right illus.).
Following successful configuration, the device will be managed by your firm.