Also, you should consider installing the Skyrim Script Extender (SKSE) available on Steam for free to efficiently utilize the mods that support it. In either case, if you download the mods from Bethesda’s official site, you should read the procedure as stated in their official support portal. Skyrim is noted to have an active adult modding scene centered around the website. In case you have a console (Xbox One or PS4), you simply need to add the mods from Bethesda’s library. For instance, if you download a Skyrim mod from Nexus mods, you need to follow their official guide to install the Skyrim mods manually. It contains a darker story than Skyrim, and was positively received by fans. It features a new race, that has come to take over Skyrim - this race is playable, and not all of them are here to invade.
It usually differs depending on the portal you download it from (for PC). Invasion of Skyrim: A vast mod, that slightly breaks the lore-friendliness (the mod author has, however, made an effort in order to fit this story into the Elder Scrolls world).
There isn’t any single solution to install a Skyrim mod. Surreal Lighting How to Install Skyrim Mods?