Sorry, I can't really help with setting up an Alcugs server (all of my experience is with UU and dirtsand). I'd be prepared for having some issues running it on a modern install without tweaking some versions. I don't see Alcugs on GitHub. Do you mean diafero's Alcugs repository on GitLab
Where it says "Debian packet" that appears to be the name of the package you should install, such as "apt-get install build-essentials" which will cover g++ and make, etc. You can combine them and do it all at once: apt-get install build-essential cmake git-core libmysqlclient15-dev zlib1g-dev
...Assuming they haven't had name changes since the instructions were written. It looks like diafero has kept it reasonably up-to-date for compiling, so that's a good sign.