Your cabin attendant will leave the proper envelopes in your cabin on the last afternoon, so you can fill them and pass them out. Just leave the one for the cabin attendant in your cabin, he/she is sure to find it.
Yes, most of the tipping is done on the last day. On the Summit, the only exceptions to that were room service (tipped each time), spa services (tipped each time), and alcoholic beverages (tip was automatically included in the price and charged to our ship card at the time we ordered the drink). Room steward, wait staff, maitre 'd, etc. were all tipped using the envelopes at the end of the cruise.