Getting 4Pane
Online Manual

Using apt to install 4Pane

Before you can use the 4Pane repository, you need to tell the apt setup that it exists. You do this by adding the appropriate url to apt's list of known repositories, /etc/apt/sources.list. You must be the superuser to do this, so either su to root (debian, PCLinuxOS), or prefix sudo to everything (or do sudo bash) (*buntu).

First you may wish to make a backup of your current settings:
cp /etc/apt/sources.list /etc/apt/sources.list.bak

Then either use your favourite text editor to add the appropriate line, or do (using debian bullseye as an example):
echo "deb http://www.4pane.co.uk/debian/ bullseye x11" >> /etc/apt/sources.list

The line to add is different for different distros/versions; choose the appropriate one:
debian bullseye: deb http://www.4pane.co.uk/debian/ bullseye x11
ubuntu jaunty: deb http://www.4pane.co.uk/ubuntu/ jaunty universe
ubuntu kinetic: deb http://www.4pane.co.uk/ubuntu/ kinetic universe

Next tell apt about the 4Pane public key (remove the 'sudo' if you've already su'ed):
wget -O - http://www.4pane.co.uk/4Pane.asc | sudo apt-key add -
or, rather faster to type:
apt-key adv --fetch-keys http://www.4pane.co.uk/4Pane.asc

You then need to do:
apt update
apt install 4pane

and 4Pane should be both downloaded and installed.

Alternatively, use an apt front-end such as synaptic to add the repository and do the install.