Read up on the following to whet your appetite. Once you have a few, specific questions regarding the topics below, I am sure many here would be more than happy to answer. :^)
> Model View Controller architecture/design pattern (you will probably get tens of thousands of hits at Google. A decent tutorial exists at this site).
> Servlets. These will handle user requests, process and then display the results in a view (JSP). There are dozens of excellent tutorials on the Net and also a decent one here.
> JSP. These will resemble HTML but also allow you to embed Java code to generate dynamic content. Again, numerous tutorials.
> Web framework. If your blog will offer a rich feature set, once you have mastered the above, consider stitching together your application with a controller framework. Two popular ones are Struts and Java Server Faces. There are numerous others, including Spring MVC, Tapestry, Web Works, and dozens more.
Focus on MVC, Servlets and JSP. Your applciation will probably, intially, grow organically. When the complexity warrants it, consider using a framework. Best of luck.
- Saish