How do I know where to position it?
Make use of the horizSizing and vertSizing fields.
For example if you want to have something at the top of the screen and 2 pixels off the right border,
give it the position 20 0
give it the horizSizing left
give it the vertSizing bottom
It's basically the direction in which the coordinates work. left goes from right to left and right goes from left to right, bottom goes from top to bottom etc
Width scalid leaves the object at the same position but if the parent object is scaled, your object gets scaled the exact same ammount of pixels.
Relative scaling scales the position and the size of the object relative to the parent.
Play with those settings a bit (note that if you set the size of the parent in the editor, it will not work, resize or drag-scale instead)