Mods customize your gaming experience. You can have custom animations, interactions, objects, clothes, hair, etc.

To install mods and custom content follow this guide: Sims 4 Mods Setup

To download custom clothes, hair, furniture, and some mods use reputable download sites such as: The Sims Resource or Mod the Sims

Depending on how you want to mod your game, you will probably need to do some research for specific things you want. I don’t recommend downloading random content anywhere you find it. Do some checking before downloading to see if other people can vouch for the source. Also, read the description for each download to make sure your game will properly load the content. Make sure you have the right expansions, stuff packs, game version, etc.

I recommend starting small by adding in a couple of items first to see if you set it up correctly. Always make backups in case your game has an issue running. There are various tutorials on YouTube that can provide you with additional assistance as well.