Needed help in starting an app and web development

I wanted to make an app and website connected in which people can book services, order items and purchase membership. Also their should be an admin panel as well for alterations in service/ items. And many more features like billing, quotation, leads sharing to the professionals received by web/ app via whatsapp API, and similarly I want the item that has been ordered to share on whatsapp API based on the product.

My Question is Can anyone please tell me from where and how to start with this development.