I want to develop a database that can be accessed by a webpage and mobile app

I'm fairly new to this so I'm unsure what are the best programs to use for the database, webpage, mobile app to link them all

The information for the database later on can be easily added by another end user in simple GUI format, like accountants with excel sheets

I think there should be something like this done before. Is there a template like this somewhere?

The program that I want to build is a database for accounting
1. accountant input number figures into a database
2. the data can be retrieved on mobile app or web page