Not +10%, just + 10 points. Anyway, the way GGs work is as follows. Those colored dots are called Gates. The effect listed under "Effects" are given to you automatically. So just by equipping that GG your Defense and Magic Defense get a +10 point boost. The Gates must be passed through in order for their effect to take place. What that means is that you must sphere change through the gate. For example, lets say you have Songstress to the west, Warrior to the north, Gunner to the east, and Black Mage to the south. You are currently a Songstress. If you sphere change to a Warrior, you will activate the yellow gate, meaning your Defense will increase another 10 points. Sphere change again to a Gunner, you will activate the red gate and you will give a +10 boost to Magic Defense. Sphere change to Black Mage and you will get another +10 boost to Defense by the blue gate. Sphere change back to Songstress and you will get a final +10 boost to Magic Defense by the green gate. The "Effects" are immediate, while the "Gates" are only available in battle by sphere changing.