Armor worn: The armor worn tells RPA which armor your character equipped. This combo box is a shortcut to equip an armor and contains only the pieces of armor that your PC has in it's gear. It is possible to equip more than one armor for your character. To do that, you need to use the Character Gear update form. Simply check the "Equip this item" box for each item you wish to equip. The Armor class will be added for each item checked. The google icon will pop up the Character Gear update  form for you.

DMG reduction: It is the damage reduction of your character.

Bonuses: The Armor, shield, size, misc, magic, etc. boxes  are all bonuses that are either calculated or specified by the user toward the total AC.

Dex(armor): The first number is the maximum dex bonus given by your dex score to your AC. The second number in parenthesis is the maximum dex allowed by your armor, it depends of the armor worn you selected.

Race: The bonus in this box depends of your character's race and  is managed by the race screen.

Magic: This box contains the bonuses of all the magic items equipped by your character that is not an armor or a shield. To have a bonus in this box, the item needs only to be equipped. See the Equipment screen for details.