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.

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.

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 .......