Stucking on LOOKUP inside INDEX

[megaiooo]

Can't remember where I downloaded this exercise, now I forget almost the knowledge of Excel's functions and go reading it again but I don't understand what it is, then I need you help for explaining how LOOKUP handles inside INDEX

Normally, LOOKUP function has structure:
LOOKUP(lookup_value, lookup_vector, lookup_result)
But in the cell "I2" of the exercise, LOOKUP function looks like:
LOOKUP(H2,{1,2,3},{2,3,4})
I understand as follows:
H2 = lookup_value
{1,2,3} = ???
{2,3,4} = ???
lookup_vector & lookup_result which I usually see in form: A1:A100, C1:C100 or A1:G100, D1:P100 ... etc.
please help me to clear it up

[martindwilson]

thats just another way of building an array of values
you could put 1,2,3 in a1,a2,a3 =lookup(h2,a1:a3,{2,3,4})
then you could put 2,3,4 in b1:b3
=lookup(h2,a1:a3,b1:b3)
sometimes you see it in match
=match(h2,{100,101,102},0) if h2 had 101 in it it would return 2 the position in the array of the match

[megaiooo]

thats just another way of building an array of values
you could put 1,2,3 in a1,a2,a3 =lookup(h2,a1:a3,{2,3,4})
then you could put 2,3,4 in b1:b3
=lookup(h2,a1:a3,b1:b3)
sometimes you see it in match
=match(h2,{100,101,102},0) if h2 had 101 in it it would return 2 the position in the array of the match

thank you very much!!!