How do I type in Gujarati font?
What do you mean?
Have you selected your default language in Tools>Options, Language Settings>Languages may need to install a specific language pack)? And set your default font in Tools>Options, LibreOffice Writer>Basic Fonts (xxx)?
In my Western European configuration, I have no Gujarati language option. Regarding the font, most “universal” Unicode fonts include the Gujarati block (it would be too long to give you a list of what is available on my system – Fedora Linux 31).
In order to type, connect a keyboard to your computer, then press the keyboard keys. That’s simple.