So you’ve added a new software source to your repos and would like to install the software contained at the source destination, but there are all sorts of messages about the key not being signed, no worries, simply issue the following command in your terminal:
sudo add-apt-repository “put your ppa address here without the quotes containing this sentence”
e.g sudo add-apt-repository ppa:freefilesync/ffs
Happy days!
Cherio