Let’s Encrypt does not work in the way you are thinking, like a traditional CA where you do some stuff with emails and submit a CSR into a webform.
The entire idea is automation. You download some software on the server you want to protect, which automatically does the validation, certificate issuance and renewal. That includes the generation and submission of the CSR.
The objective of Let’s Encrypt and the ACME protocol is to make it possible to set up an HTTPS server and have it automatically obtain a browser-trusted certificate, without any human intervention. This is accomplished by running a certificate management agent on the web server.
If you want to get a certificate the old way, there are other CAs which still support those workflows. But it’s not suitable for Let’s Encrypt, because these certificates only have a 90 day validity. You don’t want to repeat the task by hand every 90 days, right?
That’s why I linked the article. You can set it up one time, and let it run its automation into the future.