Here is a guide to CC and Mods and how to install them:
https://sims4.crinrict.com/en/2014/08/mods-and-downloads/
The guide is a little old so it is missing a step. You will need to go into the game to enable CC. To do this click on the three dots in the top right-hand corner of the main menu. This will open the Options Menu. Click on Game Options, Other, and then tick the box next to Enable Custom Content and Mods. If you are going to be playing with Mods you will also need to tick the box to Enable Script Mods. To save these changes you will need to exit the game. It is important to note that you will need to repeat these steps after every game patch as Maxis will disable all CC and Mods.
A great place to start for CC is Lana's CC Finds. They are a huge archive of CC sites and have everything cataloged in an easy to use format. They also add new content every day. http://sssvitlans.tumblr.com/sims4cc
There are also helpful threads here in the forum!
List of Maxis Match sites: https://forums.thesims.com/en_US/discussion/815146/maxis-match-style-cc-list/p1
Popular Alpha CC sites: https://forums.thesims.com/en_US/discussion/947306/list-of-best-cc-makers-updated#latest
Most CC is safe to download if you have antivirus software. There are a few creators who put their CC behind adware like Adfly and Shorte.st, be careful to close all pop-up ads and never click on bait traps saying that you need software or that Microsoft needs to be contacted. These are scams that may contain viruses. Just click the X in the top right corner to get out of them. To use Adfly and Shorte.st wait for the 5 seconds on the countdown in the right hand corner then click on Skip This Ad. The download page should then be generated.
The Sims Resource is a massive archive of Maxis CC and they never use Adfly or Shorte.st:
https://www.thesimsresource.com/
