Question

how do you write vertex form?

Answer 1

\[\large y=a(x-h)^2+k\]

Answer 2

but what number go there?
x=-1 f(x)=3

Answer 3

In the equation that @yummydum has written above.....

(h,k) is ther vertex coordinates
'x' is where your x would go
and f(x) is another way to write 'y' so that is where your f(x) value will go