Wear the headphones, or you will not be able to tell whether or not the sound is recording okay. Make sure the curved edge is pointing downwards when you put it in, or it won't go in right. To turn it off, move the slider on the bottom left edge of the camera. Please be aware that this exists, and don't use it unless you mean to.
Interviews are more interesting when they are more than five seconds long.
Any sort of daylight should be fine, dawn or dusk is not so great. House lighting is not usually all that good, but will normally be watchable. If you can see well in the viewfinder you are probably alright, but it will look a bit grainy in duller light. It's your choice. If you press one of these, an effect will be activated.