It looks like you’re running Debian 8. It’s no longer supported, so you’re probably not going to be able to install Docker or anything else.
Debian 8 has been superseded by Debian 9 (stretch). Regular security support updates have been discontinued as of June 17th, 2018.
So you’ll need to spin up a new server before you can do anything. You should move whatever you have running on that server somewhere else ASAP.