How to generate an SSL certificate for Telegram?

Question

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The telegram website says that it is happy to use this command:

openssl req -newkey rsa:2048 -sha256 -nodes -keyout YOURPRIVATE.key -x509 -days 365 -out YOURPUBLIC.pem -subj "/C=US/ST=New York/L=Brooklyn/O=Example Brooklyn Company/CN=YOURDOMAIN.EXAMPLE"

Where can I get YOURPRIVATE.key or do I have to invent it myself?
What is YOURPUBLIC.pem?
And do I need to change something here:

/C=US/ST=New York/L=Brooklyn/O=Example Brooklyn Company/CN

Answer 1

Run this command 1:1, you will have files YOURPRIVATE.keyandYOURPUBLIC.pem

Answer 2

https://letsencryptonline.com/ - Let's Encrypt generator