Back when I was starting tobookstores had basic references from publishers like Reilly's e.g. Unix in a Nutshell. You want something with a good index that you can find guides for the main utilities.
The good old days used a lot of plain text files so utilities like grep, sed and awk could handle most of the processing. Now I think you'd need more complex tools and their libraries to handle the structured text.
I think Mint has LibreOffice included already.
If not, you have the Software Center app on Ubuntu and Mint. It's like the Windows Microsoft Store: a GUI to browse for installable software.
3rd option is to install it from the command line