Process of building a data structure from scratch

Transitioning to software development here and I’d like to learn the process of building a database structure from the ground up for a project. How do you guys go about it. For example let’s say my job is to help build a website that helps my dad keep track of his construction company’s work: clients, projects, contracts, revenue, expenses etc. do you start off kind of just brainstorming all sorts of data that would be needed or do you start by asking what my dad would want to know off the website, then brainstorm off of that?

Once you think you have all the types of data (fields) that you want, do you initially just put it side by side in one table then kind of just sorting it out to try to get it into 1nf to 3nf?

Thanks.