How to take photos for an event? Please

I want to take photos of an event for a friend. I'm very amateur and haven't taken photos for long time. The event is indoors and my only equipment is Nikon speed light sb300 sigma 24-70mm and Nikon d300. Can anyone guide me with the settings? Please in much need of your help. The time of the event will be around 7.30 pm

Set camera to ISO 200, P mode. Attach flash. Shoot. As for zoom, use common sense. If you have an 18-55mm kit lens, that would do better. You'll be shooting wide most of the time due to the cramped space and the desire to get as many people as you can in one shot. If none, shoot at around 24mm for groups.