Lookup Correspoding Data On Another Sheet Of Cell Value

i have 2 sheets in my excel workbook. in my second workbook i have the values as follows

A B

ss 10
yy 20
zz 30

so in my first sheet values:

X Y

(List)
ss
yy
zz

in my first sheet X range i have list which consists ss,yy,zz
so i f choose ss from the list it has to check the valu for ss in sheet2 and has to fetch 10 and display in Y range

my excepcted output:
X Y

(List)
ss 10