Candidly share how you have used computers to assist patrons at the library. The interviewer is simply trying to understand your level of experience and how much training you should be provided if you are hired for the position. Share how often you utilize computers to assist patrons, and describe what sorts of things you are typically using the computer for when assisting patrons. You might share something like this, "I typically help several patrons each day with searching for books or materials utilizing the library's search system."