I just wanted to know if I need to somewhere sign up when an event is going to happen or just randomly post and get started.
Usually you have to sign up. In this case, there are three events underway, and two of the registrations are closed. You can still make it to the Medical Delivery mission.
And where do I go for that?
You sure? That was posted ages ago.
Yes, thats it. Be glad that it is still open, it should have started yesterday.