Researchers come to an archives with many different purposes and interests. Some have already found a listing for a specific document or collection held at that archives. Others may have a more general research topic in mind and are looking for help. What kinds of questions do researchers ask?
Some are specific:
Genealogists often do research at an archives -- they may be looking for a birth, death, or marriage record for a relative. Sometimes they know exact dates and locations, other times they may just know a name. The reference archivist can help with indexes and suggestions for other sources of information in the collections.
Another common research interest might be to study a particular person, or group, or place. The researcher may already know that a useful collection for his or her topic is located at the archives and may ask to see that specific collection. Again, asking a reference archivist might be helpful in locating other related materials that the researcher wouldn't know about.
Some questions are much more general:
For example, a professor or a student may be curious about a broad topic -- such as poetry. They may wish to find some unique, original, "primary" sources instead of working with material that's already been published. That's exactly what happened with the Poetry Here and Then project. After asking a reference archivist about collections of poetry in the Bentley holdings, the researcher discovered a variety of materials that dealt with poetry in Michigan.