So, what is perception?

Bit of a trick, that heading... if I could answer that, then the rest of the universe should be child's play!
Still, One has to try.
It's how we know about the world we live in; more especially, the environment that surrounds one. "Sense presentations" seem to be important - but not sufficient to explain everything we know; hence, Helmholz's "unconscious inferences" - the cognitive "top down" synthetic additions that one brings to the sense-evidence that one gets from the immediate environment.
Nevertheless, it's reasonably conventional to think in terms of the reception of sense data caused by our exposure to the environment, plus those cognitive 'thinking about it' bits, to help them make sense. Once we've got the hang of things, we can behave appropriately (appropriately to survival, that is).
Is that too simple? of course it is!
First of all, what is it that arrives in "sense presentations"? - it's not enough to just say "the whole thing..." - we know that, but what are the bits, the components on which we operate (along with those unconscious inferences) to understand what is being presented to us?
Notice that there is this implicit assumption that reception is important, as though perception is just like when we point a camera and microphone (and olfactory sensor, and...) at the world and simply pick up the signals that come from the environment. Is that quite right?