I consider simulating a coin flip (aka creating a so-called “even superposition”) to be the hello world of quantum computing. In a quantum programming language called Quil, this looks like

    DECLARE result BIT
    H 0
    MEASURE 0 result

This will put a 0 or a 1 in result with equal probability. ‘H 0’ is performing a Hadamard operation on qubit 0. The MEASURE allows us to extract a classical bit value out of a qubit.

Others might say the “Bell pair” is the hello world, and that looks like this:

    H 0
    CNOT 0 1

This is a bit harder to explain, because it requires understanding both superposition and entanglement.