I'm assuming you got called for Criminal, not Civil ?
Last time for me was about 5 years ago. Ya head down to the Allegheny County courthouse, they put you all in a room, and call you as needed. Turned out I got to go home at 12 noon because there were enough others and no cases to be heard. Make sure you take plenty to read !!!! You could sit for a few hours and not do anything or hear from anyone ! If I remember correctly, they make you shut off cellphones now as well. Don't quote me on that one though.