Probs with VNAV

Greetings from a new PMDG userI have had the 737 800-900 series for exactly one week and I think I have most of the "big stuff" down except for the operation of the VNAV on DESCENT. I have searched the forum for answers to my questions,but I did not find what I needed. So here goes....Assume the following: FMC is setup for a flight KORD-KLGA with the Milton 3 arrival. I have entered Milton 3 and runway 22 for KLGA in the FMC. There are three altitude restrictions for this STAR, namely MARRC at 18k, VIBES at 13k, and BEUTY at 10K/250kts. The transition point is the ETG VOR. I understand that I have to enter 10000 feet (BEUTY alt) into the AFDS prior to top of descent. What I don't understand is:1. Must I still modify the LEGS page with altitude restrictions for MARRC, VIBES, and BEUTY? 2. If I need to modify the LEGS page, does the target descent speed apply to MARCC and VIBES? Or do I have to enter a reduced speed based on altitude such as 240 kts for VIBES for example? If so, what speeds do I need to enter based on altitude?3. I thought that waypoints for a STAR were automatically realized by the FMC,and that the airplane would recognize them from the database without my having to modify the legs page. Is this wrong if you have STAR altitude constraints? I can figure out how to do the descent manually using other AP modes, but the VNAV has me confused and the manual really doesn't explain the above very well. Cheers to all and thanks in advance. Joe Swier