Adding the apt repository
If you are using Ubuntu, make sure the universe repositories are enabled
The repository is added like ever other apt repository: Create /etc/apt/sources.list.d/jitsi-stable.list
and enter the following line in it:
deb https://download.jitsi.org stable/
Afterwards add the GPG key with
wget -qO - https://download.jitsi.org/jitsi-key.gpg.key | sudo apt-key add -
and update the repository with
sudo apt-get update