Let's Encrypt is "a free, automated, and open Certificate Authority." They provide free signed certificates as a trusted certificate authority. This tutorial walks through the process of installing certbot and requesting new certificates and renewing existing ones wit Let's Encrypt. If you are just looking to generate your own quick self-signed certificates, check out my tutorial on creating self-signed SSL certificates with OpenSSL.
This tutorial will walk through the process of creating your own self-signed certificate. You can use this to secure network communication using the SSL/TLS protocol. For example, to run an HTTPS server. If you don't need self-signed certificates and want trusted signed certificates, check out my LetsEncrypt SSL Tutorial for a walkthrough of how to get free signed certificates.
Check out Security with Go, a book I recently wrote, available from Packt Publishing. It covers secure development, red team and blue team topics and is useful for developers and infosec professionals like analysts, investigators, engineers, and pentesters. It's a great book if you want to get to know Go better or if you want to start using Go for security.