When you get your
MNSSHP bracelet, head on over to the Tomorrow Land Terrace and let them know you have a dessert party reservation. They will give you a lanyard (yours to keep). They will tell you to arrive back there anytime after 8:30pm. Fireworks start at 10:15.
Tables are first come, first serve, BUT, once you pick out your table, they will put a "reserved" sign on it and that is your table. After that, you are free to do what ever you want. You can eat, drink, sit down, or even leave! If you leave, you can come back anytime and your table that you picked out will still be there for you.
Because, reserved parade viewing is not included, if you want to see the first parade at 9:15, you will need to leave the Terrace to watch it. You can only see bits and pieces of the parade from the terrace and it's far away as well. Not recommended.
My suggestion would be either 2 things:
1) Check in at 8:30, reserve your table, and grab a spot for the parade. The parade should be over around 9:45 on main street. Head back to the Terrace, eat, drink, and watch the fireworks.
2) Check in whenever, eat and drink until you are nearly sick, watch the fireworks at 10:15, watch the 11:15 parade.
Oh, and yes, you will watch them from the Terrace's ground level.