Relevant to Blender v2.31
To rotate objects, activate Rotate mode by pressing RKEY. As in Grab mode, you can change the rotation by moving the mouse, confirm with LMB, or ENTER cancel with RMB or ESC.
Rotation in 3D space occurs around an axis, and there are various ways to define this axis. Blender defines an axis by direction and a point that it passes through. For example, by default, the direction of the axis is orthogonal to your screen.
If you are viewing the scene from the front, side, or top, the rotation axis will be parallel to one of the global coordinate system axes. If you are viewing the scene from an angle, the rotation axis is angled too, which can easily lead to a very odd rotation of your object. In this case, you may want to keep the rotation axis parallel to the coordinate system axes. Toggle this behaviour by pressing MMB during Rotate mode and watch the angle display in the window header.
Alternatively, once you are in rotate mode, you can press XKEY, YKEY or ZKEY to constrain rotation along that axis of the global reference. By pressing XKEY-XKEY (XKEY twice) you constrain rotation around the x axis of the Object local reference. The same is true for double YKEY and ZKEY. As for Grab, a third keypress removes constraints.
It is possible to have a numerical imput for rotation exactly as it was for translations.
Select the point for the rotation axis to pass through with the pertinent menu in the header of the 3D window, as discussed below. (Figure 5.1, “The rotation point selection buttons”).
Bounding Box Center - the axis passes through the center of the selection's bounding box. (If only one object is selected, the point used is the center point of the object, which might not necessarily be in the geometric center. In Figure 5.1, “The rotation point selection buttons” it is on the middle of the rightmost edge, marked by a purple dot. For more on this point, see the section called “EditMode”.)
Median Point - the axis passes through the median point of the selection. This difference is only relevant in EditMode, and the 'Median' point is the barycentrum of all vertices.
3D Cursor - the axis passes through the 3D cursor. The cursor can be placed anywhere you wish before rotating. You can use this option to easily perform certain translations the at the same time that you rotate an object.
Individual Object Centers - each selected object receives its own rotation axis, all mutually parallel and passing through the center point of each object, respectively. If you select only one object, you will get the same effect as with the first button.
If you're just getting started with rotation, don't worry too much about the foregoing details. Just play around with Blender's tools and you'll get a feeling for how to work with them.
Keeping CTRL pressed switches to snap mode. In snap mode rotations are constrained to 5� steps. Keeping SHIFT pressed allows fine tuning here too. The rotation of selected objects can be reset to the default value by pressing ALT-R.
Blender Gesture System
You can also enter Rotate mode by drawing a circular line while holding down LMB.