What is actually to develop a data model?

Hello

I read in job descriptions 'you will be developing data models'. Can you explain please what this actually mean?

Is it simply to ingest data in Power BI and go to the Relationships tab and link the tables together? Or is it to build a SQL database where you need to create sys.objects, sys.tables and several other files and parameters?

And can you explain please the topics/actions you do in data modelling?

Thanks!