Most changes were in the GUI. GNOME 2 desktop has been replaced by Unity (that has been used in 12.04) and later by GNOME 3. You tagged your question "server", so I guess you don't have a GUI, so this will not apply to you.
As for command line, it didn't change that much (from command line point of view, all Debian-based systems are very similar). Probably the most important changes are introduction of new apt
command for software installation (your book will probably use apt-get
- but apt-get
should still work anyway) and introduction of snap applications - you won't find this in your book (but on a server, I suppose there are no snap applications installed by default, so you can ignore them for a while).
I don't know the exact contents of your book - as you didn't even mention the title - but my guess is that most of it should still be relevant.