A developer builds data visualizations using the package in the R programming language. They convert complex datasets into comprehensible graphs, charts, or plots, helping to interpret and analyze data more effectively. The developer uses aesthetics and layers in to create static or interactive visuals. They manipulate data using transformations, scales, and facets, and customize the appearance of the plots to make them more engaging and understandable. They also perform debugging, testing, and upgrading of the package, and often collaborate with data scientists and analysts to deliver insights from data.