Vlookup
is good if the reference values (column A, sheet 1) are in ascending order. Another option is Index and Match, which can be used no matter the order (As long as the values in column a, sheet 1 are unique)
This is what you would put in column B on sheet 2
=INDEX(Sheet1!A$1:B$6,MATCH(A1,Sheet1!A$1:A$6),2)
Setting Sheet1!A$1:B$6
and Sheet1!A$1:A$6
as named ranges makes it a little more user friendly.