Once you make a game you need to start finding about Alien Races here is a list and how to get them.
NOTE:These are not in order so be sure to read them all first.
Turians: At the very beginning of the game, talk to people about the Spectres and Saren.
Asari: Either talk with Captain Anderson, or with Avina [The VI about the council races].
Salarians: Talk to Captain Anderson after the first meeting with the council.
Protheans: CAN ONLY GET WITH TALKING WITH CAPTAIN ANDERSON AT THE BEGINNING OF THE GAME BEFORE EDEN PRIME!
Rachni: Talking with the VI near the Krogan Statue about the Krogans, the rebellion, and the war.
Batarians: After acquiring the Normandy, talk with Captain Anderson. Ask him about him becoming a Specter.
Elcor: Talk to the Elcor diplomat Calyn in the embassy. The embassy is to the right of the Human Embassy.
Geth: Ask Ashley AFTER finding her on Eden Prime.
Hanar: Either with the Preaching Hanar, or with the Shop Keeper that is Hanar. Ask him about his speech.
Keepers: Ask Avina near the Citadel Tower light.
Krogan: Automatic by watching the confrontation between Wrex and the Krogan bouncer in Chora's Den.
Quarians: Talk to Garrus in medical center.
Volus: Talk with Avina outside the embassies.
There have been complaints stating that I have copied this from www.x360a.com, which is true. I do not take any credit for this guide.