This will usually need to be solved on a case-by-case basis. ini files to make the mod operable on your computer. Of course, the mods may be installed improperly. The famous ENB shader mod provides a toolkit that lets other modders drastically change the visuals of the game - but the default installation doesn't have those changes itself. Check the mods tab of your Mod Manager to make sure that all your relevant mods are turned on.
Installing the mod with a manager may install it in the load order, but leave it disabled. Make sure your mods are enabled within Vortex. In not done properly you may be clicking on the unedited launcher instead of the modded version of the game. Foundational mods like New Vegas Scrip Extender (NVSE) may modify the launcher in addition to the game itself. Make sure you're starting the game from the correct executable. While the Nexus Mod Manager makes things pretty simple to install mods, the notoriously unreliable game means there's a variety of reasons your mods may not be loading.
