Before I start talking about what qualitative researchers do, I thought it might be useful to cover some basic definitions. Specifically, what is qualitative research? How is it different to other kinds of research?
Very broadly speaking, there are two kinds of market research: quantitative and qualitative.
Quantitative market research is generally used to measure or quantify a given variable of interest, eg how big is a market, how many people hold a certain attitude or behave in a certain way, like a particular brand, bought product X, etc.
Qualitative market research, in comparison, is used to provide understanding. Here, the inquiry is focussed on why people hold certain attitudes, behave in a certain way, or like a particular brand or product over another, etc.