Issues with for loop!

Question

The excersize says this should provide and even increasement from 0 to 20, the variable goes:
var x=20
for (;x <= 20; x += 2 ) {
document.write(x)
}
my question is what is the point of two, it only treat my answer as right when I put 2, why can't it be one for example, it makes more sense?

Answer 1

oooh I see, we don't call them even numbers in my native lanugage so I didn't realise they are called even, they call them "devidable numbers" in my language, thank you so much!!

Answer 2

Incrementing by 1 (× += 1) will print all numbers. Incrementing by 2 (× += 2) will print only the even numbers.

Answer 3

uhhh if we want an increment from 0 to 20 then we should start with var x = 0; ?