A command line argument is a parameter that is added after the executable name to pass information to it. They are a basic OS feature.
In Windows, they are typically added as part of a Windows shortcut.
Refer to the manual of the mod manager how to add executables and command line arguments for them:
-[Game Mode] for example -tes5, -sse, -tes5vr, -enderal, -enderalse, -fo4, -fo4vr -o:"[path to output folder]" for example -o:"c:\Output\" -m:"[path to INI folder]" for example -m:"c:\Users\[USERNAME]\Documents\My Games\Skyrim Special Edition GOG\" -p:"[path to plugins.txt]" for example -p:"c:\Users\[USERNAME]\AppData\Local\Skyrim Special Edition GOG\plugins.txt" -d:"[path to Data folder]" for example -d:"c:\GOG Games\Skyrim Special Edition GOG\Data\"
Replace [USERNAME] and the INI and Data folder paths accordingly for the actual setup.
Do not link to files or folders in mod manager profiles. Link to the files and folders used by the game.
Use copy and paste to avoid mistakes, like adding extraneous spaces between the command letter, colon and beginning double quotes.