In Domain Services for Windows, as in AD, there are 5 roles that are assigned to the first DSfW server in the forest. These roles are called Flexible Single Master Operation roles or FSMO roles for short.
The 5 FSMO roles are:
You can read DSfW and MS documentation to understand what each role does. Some roles are are symbolic or don't manage the directory in DSfW as they do in AD. For instance Schema Manager server. eDirectory handles the schema already. Still it a valid DSfW server has to be assigned this role.
These roles allow you to distribute one or more roles to other DSfW servers. Unless you have a large and busy domain I would not worry about distributing the roles to different servers. There could be a time were you need to move one or more roles to another server. Say you are decommission the first DSfW server in your domain and you need to move the roles to another server. Before you follow TID 7014250 on how to transfer the FSMO roles you want to verify where the roles are assigned. An easy way to see which server has all or a specific role is the dsfw_fsmo.sh script. Run this script on a DSfW server to each role and which server is assigned to each role. When finished transfering the FSMO roles again run this script to see that the new server is displayed as running the FSMO roles.
To run the script
Download the dsfw_fsmo.tgz onto a DSfW server.
untar the dsfw_fsmo.tgz
tar -xzvf dsfw_fsmo.tgz
Make the script executable
chmod x dsfw_fsmo.sh
Now you can run the script