Download the mod or CC file from a trusted source
If the file is zipped, extract it first
Open your Documents folder
Go to Electronic Arts
Open The Sims 4
Open the Mods folder
Move the mod files into the Mods folder
Keep script mods no more than one folder deep
Make sure files end in .package or .ts4script when required
Open The Sims 4
Go to Game Options
Select Other
Enable Custom Content and Mods
Enable Script Mods Allowed
Restart the game
Check that the mod is working in game