The command allows you to rotate the selected pipe. A protractor will appear to simplify the graphical angle selection; alternatively, you can type the angle manually. You can also select the "Add" option to rotate multiple pipes simultaneously

The rotation point depends on where the component is selected. For example, if you try to rotate this elbow by selecting near the straight pipe, the result will be as follows:


Otherwise, if you try to rotate the elbow by selecting the other part, it will rotate in this way: