Here is the basic lowdown on DSF/DSSH. Details can vary between releases, such as cutoff time and number of sets able to be purchased, but in general, this is how it goes:
~ Each release will have a sales time posted on the flyer. There is also a separate cutoff time, which is generally an hour to an hour and a half earlier than the posted time. You need to be in line with a wristband no later than this cutoff time - NOT the sales time. (As btown said, this cutoff time will be posted in the rules sheet that DSF puts out a few days before the release). Once they know how many people have shown up, they will put that many numbered tickets into a big raffle drum. Once they have the drum set up, people file through in the line and will receive a random numbered ticket from the drum (so you could be first in line and get number 200, or the last in line and get number 15). These tickets determine purchase order - the person with ticket number 1 will get to purchase first, the person with ticket number 10 will get to purchase tenth, etc. Once the sales time hits, they will open the shop and sell the release pins (as well as PTD pins, and chocolate and other merchandise).
~ The best place to park is directly across the street at the Hollywood and Highland shopping center. There is a big multi-level parking lot underneath the shopping center. With validation from the El Capitan theater, you can park for $2 for up to 2 hours with DSF validation and up to 4 hours with El Capitan validation. At the vast majority of pin releases they'll leave a door open so you can validate from the theater and get the four hours of parking.
~ They will specify how many sets each person can purchase in the rules, but generally it is one or two sets per person. You are allowed to buy each individual pin design in a set (so for the Villains release, if they limit to one set per person you can buy one Gaston, One Hades, one Cruella, one Yzma, and one Jafar; if you can buy two sets you can get two of each of the five pins). You can only buy one of any surprise pin that comes out, even if you can buy two sets of the previewed pins.