The metarig? Are you using Rigify?
The first thing to know is that most bones in the Rigify rig aren't supposed to be rotated. By default, arms and legs are under IK control. Facial bones are based around stretching to various move bones. Can't remember off-hand how the spine is designed.
If it seems like a bone should rotate but doesn't, first, look under the constraints tab for that bone. Some constraints will end up overriding any rotation you give them. (The bone could still be under IK control, which is a little harder to figure out, you have to figure out the structure of the whole armature for that.)
The second thing to do is look for any transform locks, on the bone tab of the properties view. Rigify goes a little overboard with its transform locks IMO. If the bone has rotation locks, it will ignore any rotation input you give them; click on the lock icons to toggle transform lock status to unlocked, if you feel like it.