A lens gathers and focuses light, without it you would have just a white photo. So the answer to your question "what is the reason for a lens" is: without a lens you wouldn't be able to see anything on your pictures
.
And for your other question why would anyone need anything else, Well.. Lets say you do sports photography (professionally) you'll need a bigger lens so you can zoom up on your subject (because you cant always be 15 feet away or whatever
) so youll need like a 200-400mm zoom lens.
But then you'll need a different lens if you want a wide angle shot of the stadium or something so you have to have like a 12-24mm zoom (wide angle)
So the only reason you would need another lens is if you cant get it from your lens.
Your camera is a point and shoot so you cant change your lens
For your last question I'm not really sure what your asking.
If you have any more questions please ask
