Alphas
The Alphas are the more aggressive ones out of everyone. They are the larger and stronger ones, the dominate ones in bed. They are the males or females pumped full of testosterone.
Betas
Betas are the normal, everyday guy. They can still breed with other Betas, but they cannot breed with Omegas or get them pregnant. With a female and male Beta, they can reproduce that way. Sometimes even a female Alpha and a female Beta would be able to reproduce.
Omegas
Omegas are the softer and gentler of these roles. They go through heat cycles, during this time they are most fertile. Once an Omega is bitten by an Alpha, they'll be mates for life. If they try to have s*x with another Alpha/s or Beta/s, they'll feel extremely sick.
HEAT
A heat is the time when the Omega is most fertile and ready to mate, or just hide away until the heat is over. If they have an Alpha mate, they will never leave their side unless they need to get their Omega food or water. Mainly, they have s*x and then rest. They keep a watchful eye over their Omega, listening to them and caring for them. But in bed, they still are the dominate ones. If an Omega has no mate, it could be dangerous to even leave the house. They could get raped, even if they protest and try to run. So, they basically lock themselves in a room and use many toys to get through this. A good part about this heat is that the Omega will self-lubricate, which means they only need to prep the Omega a bit more to have s*x. During these heats, the hormones in an Omega go all crazy. A strong scent is released during the heats, causing the Alphas to smell it and chase after the Omega. If there is already an Alpha with that Omega, they will fight the other Alphas off. Some public buildings have small rooms in their basements for any Omegas who suddenly fall into the heat and need help. Omegas can also take suppressant pills to suppress their heat.