Keep in mind i am not emo, though i used to and still sometimes listen to emo bands

As with all subcultures, research

Music, it's what makes a subculture.
Bands to get started with:

-My Chemical Romance
-Blink-182
-Sleeping with Sirens
-Set-it-off
-Get scared
-Paramore
-Senses fail
-Pierce the Veil
-Mayday Parade
-Bring me to the Horizon

Clothing:
Emo clothing was popularized by Hot Topic so that store would probably be good.
Band T-Shirts, amazon sells a lot.
Black ripped jeans.
Thrifting is always good, and you can probably find some sick band tees.