How To Set Foregin Key

I've two table.

Table
-------
stu(stuid primary key,name)=======> First table

con(one primary key,two,three,stuuid)=====> Second Table

I need second table(con) Foreign key(stuuid)....

I want stuuid this field Foreign key......

Once insert the value into first table(stu)

Automatically update stuuid this field value..

How to i'll get.* simply stuid,stuuid this two field value are equal *

Any Alter query...........

Plz help me.........