Each game is filled with players, and characters, having different knowledge and experience.
If you can get into a Welcome to the 6th World first, they will help you create a Missions character and run you through a quick job. Then you can go to the other game with "some " experience. ;-)
Regardless, know that other "newbies" will be there. If you make your character at home, using whatever tool you want, make sure you read the Missons FAQ and other information so you won't have problems.
Don't hesitate to ask for help. These boards are filled with knowlegable people.
See you at Gencon.