An advantage is a special modifier that only comes into play when you perform particular actions. When you select an advantage, you will be randomly assigned a disadvantage as well. This disadvantage will never counter any of your advantages.
If you're picking your advantages as an established character and a random disadvantage does not make sense considering established RP, contact a staff member to have your advantages/disadvantages cleared so you can reroll something more appropriate.
You can select up to 3 advantages. Make your selections by using '@assign ue'.