This is virtually the same as moving an object. First you pick the
object using either its axes or using the object selector.

Make sure you are in object editing mode (select the cube icon
in the toolbar), and select the rotation tool.



Next, select the axis which you want to rotate around. Note that
in rotation mode you can only select one of the XYZ icons. Eg, if 
you wanted to rotate an object round its Y axis (the vertical one),
make sure Y is selected.

Next, pick the rotation tool, and drag the mouse inside the edit
window (not clicking on any axes).

Back.