This is the most commonly asked question in newbie zones, likely because the first helmet reward you get looks terrible and covers up your character's entire face/head.
These instructions presume you are using the Default UI but they also have been tested with ForgeUI.
1 - In the lower left corner, click on your menu.
2 - Select 'Holo-Wardrobe'
3 - On upper-left side of Holo-Wardrobe window click the dropdown and select Costume 1 (or any other number).
4 - Click the Orange icon next to your helmet slot.
5 - Click the green 'Equip' button and 'YES' to the Purchase Prompt (which should say 0 currency)
6 - Done!
Armor - Light - Head
Item Level: 29
Bind on pickup
3 PvP Offense Rating
Madda really wants this helmet in the worse way.