Personal Package Archives are community-built and maintained linux software packages. They give the user easy access to updates and dowloads. However, because they’re not provided officially by any given linux distribution, they can pose security risks because the distribution maintainers can not verify these packages as safe. That being said however, there are a lot of useful and official PPAs that it comes down to whether or not you trust a given PPA provider. Elementary OS disables PPA support by default and if you’ve just installed a fresh copy, you’ll have to download and enable support for PPAs manually.
Enabling PPAs is pretty straightforward. Simply open up your terminal and install the
sudo apt install software-properties-common
You should now be able to add PPA repositories without errors.