Still learning linux - I'm sure there's a blindingly obvious answer to this, but everything I've tried has failed so far.
I have a single board computer (Odroid C1 in this case, but I don't think that should matter). The officially supported is Ubuntu Xenial, which I have installed fine.
I want to install OpenVPN v 2.4 on it. Neither the Ubuntu nor OpenVPN official repositories (right word?) have a precompiled package for OpenVPN 2.4, topping out at 2.3.10.
However, the Debian repository for Stretch does have OpenVPN 2.4 - see https://packages.debian.org/source/stretch/openvpn.
I think I have managed to work out that I can specify an addition source (right word?) by adding an entry in /etc/apt/sources.list.d directory. However, I can't figure out (cough, my google fu has failed to find an answer) as to how I specify the Debian repository for OpenVPN.