Hacking a website or its member section

First of all,why you want to hack a webpage?Is it a certain webpage or any site at all? There are many reasons to hack a website, or a webmaster.Maybe you want to take a revenge or maybe you want to have fun or just learn how to do it ! You can deface the website which means replace the original index with a new one or you can gain access to the member area of the site which might be easier.