Butterick’s Practical Typography
Matthew Butterick’s Practical Typography—reader-supported, ad-free, and still one of the most useful things to read on typography I know. Published on the web since 2013.
Start with “Typography in ten minutes”, five rules that will, as he puts it, make you “a better typographer than nearly every writer—and even most graphic designers”.
My personal favourites to nerd out on: straight and curly quotes, ampersands, paragraph and section marks.