how to assign selecteddropdownlist value into a textfield on selecting

my problem is when we selecting a value in a dropdown list suddenly its selected value must displayed into textbox.

how to achieve this?

solution please

and another one is when we lost focus on a text field its value must assigned to another text box.  is it possible,how

Both require javascript. For the first, you need onselect js handler, and for the 2nd one, you need onblur handler. Search on the web and you will find many solutions.

I can't get it.can you explain with one example

You can learn jQuery here and may ask there.