Well, it kind of depends. When you make a object for your UIwindow, you must specify where that object goes in your UIwindow and the size of the object.
Ex:
<Label item ="GW_ManaNumbers">
<ScreenID>ManaNumberLabel</ScreenID>
<EQType>128</EQType>
<Font>2</Font>
<RelativePosition>true</RelativePosition>
<Location>
<X>50</X>
<Y>55</Y>
</Location>
<Size>
<CX>100</CX>
<CY>12</CY>
</Size>
<Text> </Text>
<TextColor>
<R>255</R>
<G>255</G>
<B>255</B>
</TextColor>
<NoWrap>true</NoWrap>
<AlignCenter>true</AlignCenter>
<AlignRight>false</AlignRight>
<AlignLeft>false</AlignLeft>
</Label>
In the above, I put the mana numbers at location 50, 55 and the size is 100x12
When calling a graphic from a .tga file the x, y coordinate and cx, cy size specify where the graphic is and how big it is.
Ex:
<Ui2DAnimation item="Drak_MEndCapLeft">
<Frames>
<Texture>drakah_loe_groupbars.tga</Texture>
<Location>
<X>220</X>
<Y>90</Y>
</Location>
<Size>
<CX>20</CX>
<CY>15</CY>
</Size>
<Hotspot>
<X>0</X>
<Y>0</Y>
</Hotspot>
<Duration>1000</Duration>
</Frames>
</Ui2DAnimation>
Thats how I understand it in anycase. Hope it helped and didn't provide more confusion.