Integration of customize code to home assistant

Hi all,
I want to know that if suppose i am writing my own code and want to make some modification in home assistant . how can i make this reflection on my UI.
Can i write code and add to home assistant file and then when i run my hass io it show reflection on my UI
kindly let me know asap.

Thanks.

You can use custom_components https://home-assistant.io/developers/creating_components/