Display message before redirect to other page

Display message before redirect to other page

I have a simple question but yet i don't know. I would like to display
message first before redirect to other page, but my code just directly
redirect the page without display the message, or the display time is too
short am not sure.. my code as below.. pls advise. thank much.
echo "Please Log In First";
header("location: login6.php");