Mods allow you to customize your server more individually. In the following we will explain where you can find the most popular server mods and how you can install them.
First of all it is necessary to find out where to download mods for Factorio. Factorio itself offers a wide range of mods on their website. These can be found here: Factorio - Mods
On this site you have the possibility to apply different filters. For example, you can differ between popularity, category or version. It is important that the mods support the installed server version. Otherwise it is possible that the mod doesn't load or that the server doesn't start anymore.
Once you have chosen your desired mods and downloaded them, you can start installing the mods. You have to upload the mods to the server. To upload files to your server you need a FTP client. If you don't know what FTP is and how it works, please have a look at the following guide: FTP file access
The folder in which the mods are uploaded can be found under
gXXXXXX/factorio-exp/mods/. The downloaded mods are uploaded there as a ZIP file. The next time you start the server the mods will be loaded accordingly.