u only need to add several words in ur posts to put them into a certain category. And then, following a hyperlink, u can list all posts of a category.Another comment pointed to a very different but innovative approach which suggested that Blogger users can create another blog, put their categories there and then link to it from the main blog. Slightly complicated !!
Though I liked Li's approach but I am still looking for something more simple. I think I should post a feature request to the developer team at Blogger itself to add the categories feature.
P.S. On a different note, Li recommends PICO search over Google. He has some valid reasoning
I know google is the choice for most ppls, here, i recommend PICO, as i am using it. Why to use PICO? As it can index ur website when you need, and no need to wait several months for google reindexing.