Hi Stephanie! How exciting that you are planning your first trip! There is something very magical about seeing Disney World for the very first time!
This
link is a great planning resource for you on the Disney World website for planning your first trip.
As for "must sees", that will vary with every family depending on age, gender, and interests of their children. My friend,
Kim, recently answered a similar question and she gave a great list of common "must-sees" at each theme park.
I also recommend you utilize the
customized map feature found on the Disney World website. You can explore all the attractions at the different parks, choose your favorites, and they will mail you a custom map so you can start planning ahead what you think will be your family's "must-see" attractions.
Lastly, if you are feeling really overwhelmed with the details of planning your resort, dining, tickets, etc., you can call a Certified Disney Planner. These planners are no cost to you, and they have been trained to make your Disney vacation a magical experience. Simply "google" Certified Disney Planner or Disney travel agent to find one in your area.
Please let me know if there is anything else I can do to help you plan your wonderful, magical, First Disney Vacation!!