Generate your key pair
Prefix is not mandatory, you can leave the field blank and simply click on "generate".
Time required for computation increases with each character you add to that first field (if you want to use the option).
Keep safe your private key locally in a password manager or encrypted text file. Never share your private key with anybody. Never send it over the Internet in any form (text or image), not even on a private web server or cloud storage service protected by password.