How Do I Get Custom Content/Mods for The Sims 4

I don't use any CC/mods mainly because of the issues they can cause.

I can't really recommend you any sites, but they're out there. Make sure you download from a known site.

Those usually have how to's to tell you how to install the content.

And above all, make back ups:
http://sims4.crinrict.com/en/2014/09/backups/

See this for more information: [PLEASE READ] Usage of Mods and Custom Content