I take it you modded Skyrim before ? Nexus Mod Manager has been declared end of line by Nexus themselves, since Nexus now using
Vortex. The Nexus Mod Manager has been taken over by some independent modders so can still be found
here. As Uncle said thoutgh, use Mod Organizer 2 instead, can be found
here. MO2 is easier to use then Vortex unless you up for a challenge.
Been ages since I played Skyrim but you definitely need these mods:
Unofficial Skyrim Special Edition Patch
SkyUI at Skyrim Special Edition
After those just look at what mod you want to install and download them.
Yes, Mod Organizer is similar as to the Nexus mod Manager. If I remember right, when you first install MO, it ask you if you want it to download from nexus, click yes and then just download any mods you want from nexus, install them and activate them in the mod list. And I have been presuming that you have Skyrim Special Edition, if not, the above mods are also on the normal Skyrim edition site of Nexus.