Customize WooCommerce backend source code

Hello I’m new to WooCommerce,
Id like to be able to customize the add product page beyond what is allowed in the admin dashboard. It is way too complicated for vendors to setup products accurately for my purposes. Id like to add custom fields, change headings, and add custom css to simplify the UI. How can I do I go about customizing WooCommerce source code to accomplish this?

Page id like to customize:

img

Thanks