How do we know that real is real and that it exist and that it is true?
Objective reality is what will not go away even if people stop believing in it.
To be distinguished from "inter-subjective" reality, consisting of many socially constructed belief systems which disappear the moment people no longer believe in them, like religion, law, countries, corporations, government, values...
Reality is the natural order which is generally assumed to be intersubjectively present for us all, and apprehending it accurately is the goal of constantly developing a better and better mental model of that external world. What "better" looks like in this context is, to boil it down to something simple, is "fewer surprises". That is, following one's understanding of how reality works should lead to expected outcomes more often than without that understanding. If your understanding of reality often fails to explain or predict experienced reality then it likely needs revision and improvement.
There is no such thing as 100% objective truth and even if there were, our brains are extremely sloppy, noisy and imperfect ... so understanding reality is always a progressive work-in-progress involving constant refinement and both individual and group effort.
Religion, generally, is an attempt to short-circuit this effortful process of continuous improvement using canned abstractions and/or metaphors as a basis.
What it is: complex, amazing, governed by scientific principles of which we only comprehend a tiny sliver. It is what physically IS. Reality discovery is the "Holy Grail" of science.
At least as important a question is what reality is not. It does not equal our perceptions of it, because we are flawed and easily misled. It also is not "Truth," which is a value-laden term that varies with our personal values, priorities, and perspectives. ..As in "find YOUR truth."