First add the oxen.io apt repository to your system:
sudo curl -so /etc/apt/trusted.gpg.d/oxen.gpg https://deb.oxen.io/pub.gpg
echo "deb https://deb.oxen.io $(lsb_release -sc) main" | sudo tee /etc/apt/sources.list.d/oxen.list
Update your apt package list:
sudo apt update
Install the lokinet-gui package:
sudo apt install lokinet-gui
This will also install and start a background service called lokinet.service that can be controlled with the lokinet-gui application.
Simply jump into the lokinet-gui client and click the large green power button.
Head over to Exit nodes or Accessing SNApps for an overview of the exciting things you can do with Lokinet up and running!
See the troubleshooting guide here if you have issues.