When writing the Windows installer for 1.8.0, I forgot to include the new “Guides” folder, which contains the materials templates and the how-to guides for building ships. This will be obviously fixed in 1.9.0, but in the meantime you can either download the ZIP package of the game (which does contain the guide), or pick your files from the Guides directory of the GitHub source code, at https://github.com/GabrieleGiuseppini/Floating-Sandbox/tree/master/Guides.