Since you entered this as an array formula, excel will do essentially "for each
cell in this range, do something" comparisons.

rng_lookup_1=value1
will return an array of true/falses depending on whether each cell matches that
value1.

The same thing will occur for each cell in rng_lookup_2 compared to val2.

So you're left with an array of true/falses multiplied by another array of true
falses:

{true, false, true, false, true}*{false, true, true, true, true}
for example.

When excel multiplies booleans, it'll result in an array of 1's and 0's.

In my example:
{0,0,1,0,1}
(true * true = 1, false * anything = 0)

=match(1,{array of 0's and 1's},0)
will return the first position in that array that matches 1 which means it
returns the first position that matches value1 and val2.

=index(rng_result,somenumber)
will result in the somenumber-eth element of that rng_result range.

Simple as pie, huh?

But very powerful.