How to extend a plugin like we do a theme?

In WordPress we can easily extend a parent theme by creating a child theme. How can we create a child plugin from parent plugin?

I search a lot and people suggested to use actions and hooks but what if a plugin doesn’t provide hooks and actions?

Actually I want to extend LearnDash plugin. I want to extend it’s functionality in my child plugin. So that if any updates comes in plugin, it shouldn’t conflict with our custom changes. But currently I have no idea how to extend it?

There’s no standard method apart from hooks, and it’s up to the developer of the original plugin to add and support these. If the plugin is extendable they will have developer documentation (LearnDash’s is available here). The specifics will depend entirely on the plugin and how they’ve chosen to allow it.