Duck DNS includes step by step instructions on how to set up their service on a wide variety of operating systems. There even are instruction on how to set it up on raspberry pi, mikrotik routers, tomatoUSB as well as multiple ways for Linux, Windows and OSX.
You do get to use all features of Dynu services with a free account. But if you need to use say 300 hostnames, you may need to pay $9.99/year membership fee. Usually, a free account is more than enough.