Difference between शिक्षक and अध्यापक?
What is the difference between शिक्षक/शिक्षिका and अध्यापक/अध्यापिका?
Which one is used more often?
Can शिक्षक have feminine gender too?

Question

Difference between शिक्षक and अध्यापक?
What is the difference between शिक्षक/शिक्षिका and अध्यापक/अध्यापिका?
Which one is used more often? 
Can शिक्षक have feminine gender too?

Answer

Shiksak is more usable and common words meaning your guidance but adhyapak means only educational teacher

and yes both shiksak and adhyapak both are feminine gender.

Answer

Shiksha has a broad meaning( music, literature, subject etc), Shikshak gives or shares knowledge with you. (शिक्षा देने वाला )
Adhyapak is limited to teaching a chapter/s. (अध्याय पढ़ाने वाला )

Both are used commonly.
And yes Shikshak & Adhyapak both has feminine gender.

Answer

Well, here it means Teacher
 शिक्षक/अध्यापक  (Male Teacher)
शिक्षिका/अध्यापिका (Female Teacher)

It doesn't mean Headmaster/Head Mistress or Principle or Professor .

Hope able to make you understand .......