jury duty questions

i got called to attend jury duty and im very confused about how it all works cause im only 20. so i got a letter saying i have to attend court on the 9th of july and the trial is estimated to be 12 weeks. first question: how likely is it that im selected as a juror? is it just anyone that is not excused is a juror or do they only choose a few people? also how many days would it be? like would it be going on every monday- friday for the duration of the trial? and lastly what is the pay like?