You will be provided with a domain name looking like xxxxx.ubucon.abolivier.bzh, which points to your dedicated VPS.
To access the server's command line, run ssh [email protected] from a terminal (or connect with your favourite SSH client with the user ubuntu), and use the password ubucon2019.
wget -qO - https://packages.matrix.org/debian/matrix-org-archive-keyring.gpg | sudo apt-key add -
sudo add-apt-repository "deb https://packages.matrix.org/debian/ bionic main"