Players than just have to follow the Mod Engine's instructions to set its directory to whatever folder they will be putting their mods in.
All players have to do is download the Mod Engine and copy its files inside the same folder that the DarkSouls3.exe file is in. This addition to the game will make downloading and installing mods an incredibly simple process. Once here they will be able to download the DS3 Mod Engine. Those who do want to mod the game though should first make their way over to Nexus Mods and set up an account for free. The best practice is to just stay offline when using mods anyway. More than this though players should not use mods that give them an unfair advantage over players anyway just to be polite. Players should keep in mind that installing mods is technically against the user agreement for Dark Souls 3, and they can technically be banned from online servers if mods are detected in their game while online. In the past this made modding the game fairly difficult, but thanks to significant work by the community it is now easier than ever to add mods to the game. From Software does not officially support modding for Dark Souls 3, and are actually very much against the concept.