Well I always say google is your friend. Here is the manual download page for you servo. And since you are on the UCCNC forum I'm going assume you have one of their products!
So if for example you have the ETH 300 then the step and direction outputs are 5 volts then you connect them the the corresponding pins of CN1 as per the manual.
Here is a link to the manual if you do not have it.
https://www.omc-stepperonline.com/t6-se ... 0h2b3-m17s