Rotating a selection

There are a few ways to rotate your selection. The easiest is to make a selection around your object, then hold down ctrl + t (WIN) or cmd + t (OS X) to initiate the transform tool, then you can rotate your object freely, or by holding down shift, snap to 45 degrees.  

You could alternatively use the "tile placer tool", which offers more specific rotation implementations that could achieve the same results as above. Select the "tile placer tool"; notice if you hover the mouse over the icon, you can read how it works. Right click on your canvas to pick the current tile from the canvas, then you should be able use the transformation properties above, which has various angles displayed, flipping etc... choose 90 degrees and click no the canvas again.

I hope this clarified some things for you :)