Great question, @ghulammujtaba! WordPress is written in PHP. If you'd like to develop plugins, themes and the like, you need HTML, PHP, and CSS knowledge.
There are many tutorials online for developing themes, and you don't actually have to start from scratch. WordPress has a number of frameworks to work from. I think Genesis is the most well-known, but there are many.
Here's an up-to-date article on a few - https://athemes.com/collections/best-wordpress-theme-frameworks/
If you're interested in learning, I would start on YouTube.
Thank you so much for your reply @prowebwriter, I have actually started learning some coding skills and saying to goodbye to accounting and finance field where I wasted almost 18 years. Will be in touch with you for sure!
Chase your dreams! Gave you a follow to make sure I don't miss it. 🙂
Thanks @prowebwriter, I will surely poke you in the future, will have a lot of questions for you.