When you are learning about the various web technologies, it is always easier to install the the web server on a local computer and experiment there. It is also a great strategy for designing the website or web app at local computer first and then uploading it to an online web server.
For doing these experiments, it is always a good idea to use web server packages like EasyPHP which packs all the most popular web development tools such as Apache web server, Nginx web server, PHP, MySQL, WordPress, phpMyAdmin and more. You can choose which of these components and which of their versions you want.
But if you also want to experiment with SSL certificates which are installed on a web server for end-to-end encryption of its web traffic, then you can also learn using OpenSSL and how it is used to generate certificates and keys. One easy way to learn about OpenSSL is through YAOG which stands for Yet Another OpenSSL GUI. It is a GUI front-end for OpenSSL command line tools. For understanding and downloading the latest version of OpenSSL, you can visit https://www.openssl.org/.
YAOG package comes with OpenSSL command line tools but they are older version and you can update them yourself by simply copying the newer files. Nevertheless, the basics of OpenSSL are the same. You can use it to create CSR, certificates, keys and more.
On the left side of the YAOG interface, we can find the tools to generate CSR and key pair. We can also test the certificates with the keys using the tools provided. Similarly, on the right side we can find the tools to generate the private and public key pair. We can use choose key type, key length and cipher type for these key pairs. Fruthermore, it also gives us tools to test existing key pairs.
You can download YAOG from https://github.com/patrickpr/YAOG.