What do I need to drive a servo motor?
“I assume it [inability to run servo directly from mocrocontroller]
  has something to do with power.”


You’ve probably answered your own question.  Most motors useful for robotics consume more current than a microcontroller pin can source or sink.  (Unless, you’re building a micro-miniature robot.)  As a result, the motor requires a power driver, such as H-bridge made with power transistors.  For an example of an integrated H-bridge driver, see L298 (dual H-bridge) and A3966 (application note).