It ain't easy
I was excited about running a tri-OS laptop. The latest ChromeOS computers run most Android apps really well (contrary to the nay-sayers) but Linux support is still rudimentary and in beta. Linux makes sense, because it's free and, more significantly, ChromeOS and Android are built on Linux.
Once you turn on Linux in ChromeOS, all you get is the command prompt of Terminal. I tried a few times to get a GUI running, such as a Linux desktop or a word processor. I failed, partly because the instructions I found online were old (tutorials from August are old) because Google has been updating the Linux system. After Christmas, I searched again, and this time was successful.
In my case, the solution took two steps:
Step 1. Remove a locked folder so that software would install:
sudo rm /var/lib/dpkg/lock
Step 2. Install the Gnome package installer:
sudo apt-get install gnome-software gnome-packagekit
With the Gnome package installer, I was able to install some GUI-based software. But in the end, I found that Linux support is not complete in ChromeOS, and so programs tends to run slowly and awkwardly.