The rotate tool in SketchUp (keyboard shortcut Q) is used to easily rotate and copy items. First select the item you wish to copy and activate the rotate command. You will then see a protractor on your screen. This protractor changes color with the orientation of it on different planes. If you want it to stay oriented to a certain plane make sure it turns the color you want and hold shift. This will lock it on that plane and you can then move the protractor to whatever location you want to start the rotation.
Click where you want your pivot point to be. Then select where you wish to grab the item. Then move the mouse in the direction you wish to rotate and click where you want to stop. You can also specify a certain angle and press enter instead of clicking to drop the item.
During this whole process you can also copy the original item in the rotation by pressing the “Ctrl” button on your keyboard. This will activate a copy of the original item and you will see a + sign next to the cursor.