Firstly i would like to start with what blog and a normal website mean. A blog (weblog) actually a e-dairy, like your daily dairy, through which you can express your feelings and write your experiences. Blogs can be of 2 types : public or private. A public blog can be viewed by all the users on web but a private blog can be viewed just by its authors(just like a personal diary) . Today most of the blogs are used are public and used for information/knowledge sharing purpose. Blogs are used when the content is not static and needs to be added or modified on regular basis. The blog scripts are readily available for free and needs only to be installed on a webspace. You can download one from Wordpress. Or an alternative is getting a free preinstalled blog from Wordpress or Blogger

Talking about normal websites, it is used wherever the content is static, in other words the content is not changed regularly. I prefer blogs for the following reasons :
->various predesigned blog themes (templates) are easily available. U can choose required design for ur blog just at the click of a button(template chooser) . If ur using a website u need to edit ur files to change their appearance or use website editing software on your pc.
->There is no need for uploading an stuff (exept images). Inbuilt editor allows you to add content directly and saving it. Websites need their files to be edited and uploaded many times.
->Easy interaction with users using "comments" . Normally websites use communication through email (non server side execution scripts).