It's evident that the main part is XYZ, which lets you change the position, the size, and the rotation of the frame:
Horizontal positioning from left page border is made with X-pos
Vertical positioning from top page border is made with Y-pos
In both, the Basepoint lets you choose which corner will be used for the calculations.
Positioning the object can require object stack changes. You might sometimes have some text above an image, for example, and you would want to be sure that the picture won't hide the text. In this case, the Text Frame should be placed above the Image Frame. Green Level arrows and the XYZ tab let you change this as you wish.
If you're really fed up with rectangle frame, you can easily change it afterwards. Once your frame is on the page, just go to the Shape tab of the PP. Here you'll see the Shape label with a square button at its right (see the following image). Clicking on that button will display a list of default shapes that you can use...