Originally, typesetters manually arranged letters for printing; now, it's mostly digital. Decades ago, he would have been manually arranging letters as a typesetter.
Pro Tip 2/3
Technological Shift
Modern typesetters are likely to use computers, not physical type. As a typesetter today, she designs the page layout on her computer software.
Pro Tip 3/3
Publishing Link
Typesetters are important in publishing; they ensure the text appearance is correct. The typesetter made sure the book's text was perfectly aligned.