What is Emo?
Emo loosely defines Emotional or emotive hardcore, and it's a style of hardcore punk rock music that originated in the late 80s and 90s.
this is what oldschool emo is
and this what oldchool emo looks like 
Later emo evolved and developed into something called metallic hardcore.
where metal and hardcore were mixed, emo began to emerge as this
Emo Fashion
Eye liner, makeup and body and facial piercings, band t's and black clothing all is emo.
Long black hair with a side fringe is usually seen as emo as well, or wavy stylized hair like this girl below 
an emo shop would be hot topic, emos tend to wear black hoodys or black skinny jeans. .
Emos also tend to wear skinny jeans and sometimes baseball caps reversed or in some sceney douche style 
Emo Music
Emos or most emos listen to Slipknot,My chemical romance, fall out boy, paramore, motionless in white, pierce the veil, bring me the horizon, asking alexandria and etc....
here's some great starters ........
also fallout boy and paramore are more pop-punk emo
Emo Activities
Emos tend to play video games or do art, or manga sketches.
drawing manga cartoons from their favourite anime, like for instance attack on titan,
Most Helpful Opinions