Coding your material and grouping the codes into themes: patterns of meaning that answer your research question.
Key thinkers: Virginia Braun, Victoria Clarke, Richard Boyatzis
The longer story
Thematic analysis is the workhorse of qualitative research—you're looking for patterns across your data. Read through, notice what recurs, develop codes, organise codes into themes. Braun and Clarke's six phases give you structure without straitjacket. The themes don't leap out; you build them through iterative engagement with the material. Good themes capture something meaningful for your research question; bad themes are just categories. It's flexible, accessible, and works with most qualitative data. Start here if you're not sure what else to do.