Chord Sheet Maker Online is intended for "chords only" sheets, so adding lyrics alongside the chords is not supported.
That is very straightforward. There is a button lyrics edit which takes you to a form where you just add the song text.
There is nothing special here. The font size is automatically adjusted to the maximum size. And that's it.
On a large screen you can display the lyrics sheet alongside the chords sheet.
That might be useful for practicing songs.
See as an example Amazing Grace
If you add your charts to compilations you can create different variants of these.
See as an example a compilation of some Traditionals.
Despite the fact that you can literally find any lyrics in multiple places on the internet, it is not allowed to publish any text without permission from the copyright holder.
As a result, lyrics are only shown for some traditional (public domain) songs on this website.
But of course within your user account you can add lyrics as you like.