Hi! What do you mean by "square rounded tool?" If you mean the rectangular and eliptical marquee tools, then when you have dragged it around something to make a square or round selection, you can right click inside it and then choose, cut out, or copy, and then paste it in to wherever you want. Is that what you mean?
2nd that Vafann. If you mean the shape tool, square with rounded edge, no, it's not a selection tool which is what you're describing. But you can get a square with rounded edges selection by using the rectangular marquee and a big amount of feather. Go to select>modify>feather.
When you make selections you can go to edit>clear like Vafann said. You can choose to clear what's outside the selection. select>inverse. You can copy and move or just move the selected area/item. You can make a new layer either by copy or cut. Those are some basics. Hope we helped.
If it is the shape tool, it can still be done.
Make sure that path is selected in the options bar, make your selection. Go to the paths palette and from the flyout menu select Make Selection, select the default. The path can now be deleted and you now have a selection to do as you wish.