There are several ways to mod most games, many have in game configurators for mods, however these are rarely the best way, and for that reason Mod Managers exist.
There are several popular ones for a variety of games, Vortex by Nexus Mods, NMM as the predecessor to Vortex, Mod Organizer by Tannin, and Wrye Bash by the Wrye Bash Team.
NMM and Bash are not very well supported right now, but MO2 and Vortex are, MO2 is being covered already by several bigger channels, so I figured I would cover Vortex instead.