In multiplayer, each class has a special Veil ability. Medic's have Healing Aura, Engineer's have Veil Speed, and Soldier's have Veil Strike. Now, first you need to earn some money (Approximately $1500)
Now that you have your money, you need to go to the Rewards section of the main Multiplayer menu, then go to the class sheet to find it's Veil Ability. After buying a ability, (One per class) you can now use it in multiplayer. To use the ability you need Veil power, which you spawn with. Then hit the Up D-pad button to activate it. All you need to do is use each one once. For Veil Strike, you do not need to get a kill with it.
The achievement wont unlock until the match is over.