OpenSSL step by step tutorial explaining how to generate key pair, how to export public key using openssl commands, how to create CSR using openSSL and how to generate self signed certificate using Open SSL command line tool.
To dowload openSSL visit: https://www.openssl.org/

To learn how to use Java Key Tool to generate self signed certificates:    • How to Generate Key Store Using Key T...  

To learn how to use Portecle to generate self signed certificates:    • Generate Self Signed Certificates Usi...  

To learn difference between oneway and twoway SSL:    • How One Way and Two Way SSL Work| Mut...