How can I start Plugin Development?

You need to learn how WP is ‘built’ and functions. An understanding of that will help immensely.

Start at the Codex https://codex.wordpress.org/ . Lots of information about everything WP. And there are lots of googles/bings/ducks about creating plugins.

Start with a simple plugin that changes a minor thing (like changing the ‘Howdy’ to ‘Welcome’ on the admin screen. Then try a Settings page that stores things in the wp-options table. Again, lots of tutorials on plugins.

This is not an easy or quick ‘journey’, but lots of fun if you like tweaking and programming things.

Good luck!