If you have a .pak you put .pak into: C:\Users\User\Documents\Larian Studios\Baldur's Gate 3\Mods
Then edit modsettings.lsx in notepad that is located in C:\Users\User\Documents\Larian Studios\Baldur's Gate 3\PlayerProfiles with the appropriate line included in the mod readme.
You can't put non-pak into their respective folders because those folders are archived inside the .pak files in the game.
You can make your own pak files with Larian export tool from the files you downloaded however. There is a button to create package.
https://github.com/Norbyte/lslib/releases/tag/v1.15.1Edit: Also if you want to brute force it completely, you unpack the original .pak files of the game, insert your modded files in and then pak it back up, but upcoming game updates will check for version missmatch and remove your mod.