Do you mean a modal window or Open Url window? If you going for the later, You can use the below setup.
For Modal window, you may need to create a new format in skin rule and specify the top, left, right alignment. You can also specify height and width for the same.
For Open Url In window, You should be able to specify the window name, if left blank it will open a new window, if you put "_self". it will open in the same window. You can also specify the width and height for the same.
If you want to align it to a particular position in the screen, you can specify the Top and Left value (how much spacing from Top and left) for the new window etc.
You can try these settings and see which configuration suits bests for you.