to start, there are an uncountable infinity of them so 100% are not representable. Also when notated typically, there are 2 representations of lots of numbers.
"Why should I believe in a real number if I can’t calculate it, if I can’t prove what its bits are, and if I can’t even refer to it? And each of these things happens with probability one! The real line from 0 to 1 looks more and more like a Swiss cheese, more and more like a stunningly black high-mountain sky studded with pin-pricks of light."
This is an interesting question to answer in a way that works regardless of mathematical background; let me try something a bit handwavy.
The way people are taught about the real numbers is typically a progression, you work with integers as a child, get your head around negative numbers etc., eventually you are shown "algebra" and equation solving, and you will be introduced to "roots" as solutions. You'll learn about e.g. sqrt(2) as the solution to 2=x^2 and probably have some discussion of irrational numbers then, rather than rationals, but it may miss most details. If you study in university at all you'll probably get some sort of lecture on countable vs. uncountable infinities and probably not look too closely unless it's a pretty mathematically oriented class.
Along the way you'll also be introduced to "special" numbers, pi and e at the minimum, usually motivated from somewhere else (e.g. we "found" pi due to geometry, e comes from logs, etc.).
So the picture you get is that you have all the "normal" every day numbers, then some more a little bit weird like sqrt(2), and a few special ones like "pi" and "e" that are useful.
Truth is, from the point of view of the reals, this is all backwards.
Numbers like 1,1/2, sqrt(2), etc. are called "algebraic" because you can find a polynomial equation with integer coefficients that has it as a solution (so x^2=2 means sqrt(2) is algebric, x=7 means 7 is, etc.). Anything non-algebric is called transcendental. Pi is transcendental, as is e, which means no matter how hard you try you can't find a polynomial of that type such that ax^n + bx^n-1 + ... = pi. It turns out to be hard to prove that something is transcendental, we have only proven a double handful or so.
So the weird part is transcendental numbers are "almost all" of them. In a technical sense: the set of transcendental numbers has measure 1 in the field (of real numbers,o r complex for that matter).
One way to think about it is if I gave you a bucket containing the real numbers between [0,100] and you randomly picked numbers out for the rest of your life, you would expect to never pick an algebraic number.
So all the numbers all humans use for day to day math and accounting, as well as most scientific math, etc. (obvious pi, e and friends contribute) ... all those number come from a subset of the reals so small as to be negligible in the grand scheme of things. To a first approximation, the reals consist of numbers nobody ever uses :)
The reals are stranger than most people realize.