I have seen is several web sites that they have a new style of adding a pop up box.when goes to site. The backgroup goes darker and pop up comes with a nice close button. Most sites use them to add subscription options. I cant give an example site as the site I have seen doesnt display this again. I am sure may of you must have seen this. What is this? is this CSS?
you can use this code also <script>alert( "hello");</script> . This is a basic pop up . But you can add images and give its border and height.
Its better not to use such pop ups at the entry level of your web visitors. Pop ups only annoys people. You can add a pop up in the exit levels that means when a visitor is going to leave your site. Second most important thing don't add a subscription option by popups which will discourage your visitors to visit your site later on. You can offer some free ebooks or free samples instead.
The first thing your going to need to edit is the address, the code above is set to go to Yahoo, change this to the address of the page you want to pop-up.