You could write a LinuxDoc document without having any LinuxDoc software. However, it's likely that it would contain some errors in the tags (or their use) so that it would be returned to you for correction. Even if there were no errors, the results might not not look quite right. So it's best for you to have the software to convert your source code on your computer.
The Debian distribution of Linux has a linuxdoc-tools package. There is also a rpm package for non-Debian distributions. It was formerly called sgml-tools. Don't use the sgmltools-2 package which is primarily for DocBook.
To use it, you run converter programs on the *.sgml files. For example to get text output, type: "sgml2txt --pass="-P-bc" --blanks=1 my-HOWTO.sgml". To get html output, type: "sgml2html my-HOWTO.sgml". If it shows errors, it will show the line number and the column number where the error is in the source file. Typing "man -k sgml" should show you a number of other programs with a one-line description of each but not all of them are for linuxdoc-sgml.
For sgml2txt, the option --pass="-P-bc" is needed to get pure text output since otherwise you get text output which puts emphasis on words that need emphasis: by overstriking for old impact printers (avoided by the "c" option in -bc), or by sending escape sequences (avoided by the "b" option in -bc) to terminals.
In case you are interested, the --pass passes the -P-bc option to the groff program (used by sgml2txt) and the -P option of groff passes the -bc option to grotty (a post processor for groff forcing grotty to generate just plain text output. What a mess! The default should be plain text so that all of this passing of options wouldn't be needed. If you don't use this --pass ... option then if you use the Linux "cat" command to display the text, it looks great. But using pagers or editors on the text output file usually results in the escape characters being eaten so you see a bunch of unwanted characters in your texts that were supposed to be the "sequence" portion of the escape sequence.