After installing, you can try it out for 180 days. After 180 days you and your system will run into troubles for sure. But the good news is: You can extend the period to another 180 days up to 3 years.

Extending the Trial Period

First, take a look at your desktop. You should see the countdown in the corner down right.

Or start PowerShell and run slmgr.

1slmgr -dlv
Pay attention to the Timebased activation expiration and the Remaining Windows rearm count. You can rearm the period 6 times. (180 days * 6 = 3 years).

When the period comes to an end, run slmgr -rearm to extend it by another 180 days.
1slmgr -rearm

Next restart your computer.
1Restart-Computer
Once restarted, open PowerShell and check your settings.
1slmgr -dli

Important Note
The evaluation version may not be used for commercial purposes. Have fun playing with the Windows Server 2016 Evaluation Version!
By the way: You can do the same with Windows 10711. But the Windows 10/11 Evaluation Version can be used only for 180 days in total.