Every page has a Contact link in the footer, and it is there because your side of this is wanted, not just tolerated. A typo you caught, a passage that confused you, a study that is not loading right, a question you cannot find the answer to: all of that is worth sending.
Click Contact and you get a short form: your name, if you want to give it, what the message is about, and a plain box to write in. Submit it and your own mail app opens with the message already written, ready to send from your own account. Nothing is submitted to this site and no outside service reads it first.
Reading an essay and want to write to the person who wrote it? Click the author’s name under the title. It takes you to that same Contact form, already opened with that essay named as the topic, so your message arrives saying exactly which piece you are writing about without you having to explain it.
Whichever door you came in through, do not talk yourself out of sending it. A short note is enough. If something helped you, say so. If something did not, say that too.