Why are we the smartest species on the whole known universe? Why?

One possible reason would be because intelligent give humans, and only humans, evolutionary edge compared to their peers. Gorilla, for example, are strong because strength give Gorilla evolutionary edge. For our species, that's intelligence. But how?

What evolutionary advantage does having high "intelligence" does to humans?

My friend told me that the greatest benefit of intelligence is that we "deceive" others betters.

Is that the main use of intelligent?

Deceiving others? Many of my mensa friends are honest. If anything I hate lies in any form except for jokes. Also we don't seem to have more children than normies.

How does having, say, high IQ help a person reproduce?
The evolution of higher intelligence in hominids is an empirically difficult enough evolutionary question that (a) it might be better for biology.se and (b) any answer needs to be taken with a pinch of salt, but I'll give you a feel for it. By that I mean, "watch the way multiple accidents of evolutionary history made evolution more favourable among our ancestors than most animals".

The 2003 documentary Walking with Cavemen discussed one model of what happened to early hominids: a decline in African rainforest coverage c. 8 Mya led to arboreal primates evolving bipedalism for more efficient locomotion, and this meant hands no longer compromised between movement and tool usage. Hand-brain co-evolution would have involved a positive feedback, which may (or may not - always bear that in mind) be part of the reason for rapid brain growth among Australopithecines. The same documentary also discussed how subsequent climate change in Africa changed the ecosystem enough to provide new nutrition opportunities for early Homo species, and how the move from North Africa to West Asia led to bamboo tools.

There are many models for what encouraged the evolution of higher intelligence in our ancestors, at various points in the past 5 Mya or so. The reason a trait is more favoured in one species than another comes down to unique cost-benefit analyses. Large brains are expensive, but the shift from a mostly herbivorous diet to one more reliant on meat, especially bone marrow (which only hominid tools could access), is part of why they were "worth it" in our genus.