Creating a popup page in HTML

Creating a popup page in HTML?

Hi for my website there is a link to about.html I want about.html to basically give info about the site etc. Now I want about.html to open in a popup manner, how would I do this?

An example of what i want is on this site: http://www.dadewear.com/shop.html

When you click on "BIO" it opens up as a popup, that is exactly what I want for my site, please give me the exact code as I cannot find it anywhere

Thanks!