Mecha is like a robot I can climb into to fight the omnics. My squad and I fought for South Korea. We were the best! (D.Mon and I were the top two, but don't tell the guys. Don't want to hurt their feelings too much.)
A stream is- well, you watch television and games and such right? Well a stream is a televised event. I'll play games and stream it so others can watch me. I'm a top Starcraft player where I'm from. (That's a video game.)
We were fighting omnics. Its a long story but they were robots that didn't want to serve anymore. They did a lot of destruction. So I hope that answers everything for you!