To take an idea from inception through to fruition, you should follow a design process. This process essentially says "think before you act." Discuss rules, requirements, and objectives; then create the final version of your normalized tables.
In this chapter, you saw how forums are hierarchical in natureforums contain topics; topics contain posts. You can't have a topic without a post, and posts don't exist in forums without belonging to a topic. You applied this knowledge to the creation of tables to hold forum topics and posts, and used PHP scripts to create the input and display pages for these items.