I highly recommend Vortex since it has a great UI and built-in tools to easily manage mod file conflicts. These tools automatically handle most mods' installation, so you don't have to dig around in-game files - simply drag-and-drop compressed mod files, and the mod manager will do the rest. The first thing you need is a Nexus Mods account, the website where most mods are posted.
That being said, there are still a few tools, engine improvement mods, and more that you'll need before you can start modding. Since Skyrim SE is an updated version of Skyrim with more modern tech under the hood than the original game, preparing to mod it is easier than it is for older Bethesda games.
Source: Bethesda Game Studios (Image credit: Source: Bethesda Game Studios)
