"Going to Alaska 8/17, what tours do I need to book now thru Princess?"
Your best bet is to go through the tour descriptions in the book and to reserve whichever excursions you want to take on Princess's web site. The tickets should show up in your stateroom on the first day of the cruise and be billed to your shipboard account. If they don't for any reason, just go to the shore excursion desk and obtain duplicates.
If you change your mind regarding any tour, you can return your tour ticket to the shore excursion desk for full credit and, if you wish, book a different excursion in that port of call until the "closing time" for tours in each port. The "closing time," published in the Princess Patter, usually is around 10:00 AM on the day before the day of the port of call.