While most games require 3rd party software to mod your server, several games are utilizing the Steam Workshop. While the main purpose of the Steam Workshop is to host a catalog of mods it also provides the capability to create lists of mods that you manually select. These lists can be configured to your server, which configures your server to download and use those mods automatically.
Before you start it's recommended to use Steam from their website, rather than your Steam client installed on your computer.
Creating a Workshop Collection
First make sure you are logged in on the Steam Workshop. Find the game you want to create a collection for and click on it. This will take you to the game's workshop page.
Now that you're on the game's workshop page you'll need to go to the Collections page. You can find it's link under the
Browsetab. Once you're on the Collections page you can either find a pre-existing collection or create your own using the link on the right.
Once you've found the collection you want to use you'll need to get the Workshop Collection ID. When on any collection page you'll need to find the ID from the URL in your browser's address bar. In this example we have bolded and separated the ID: