Categories are just a way of organizing your entries.  Your entries will display as normal even if they are marked with a category.  They will still move down the page as you add new entries.  The will still be shown as normal in your archives list.

"But wait," you say, "then why would I want to use them if they don't do anything?"

Here is what they can "DO".  They can help other people find related entries on your blog pages.  They can give your reader an idea of the entry type at a glance.  They can help you to find your older entries easily.

Okay, let's say I have a recipe that I want to add to my blog but also want to put it into a category with all my other recipes. I type my blog entry and mark it with my category. When I post, the entry will appear under my main page as a normal blog entry and a link will be with it for my categories title of "Recipes". This entry will act like all of my other blog entries.  New entries will push it down the page like normal and it will still be in my archives with all of the others.

The only thing that is different about this entry is the link for my category.

When someone (including me) clicks on the link for my "Recipes" category…. Only my recipe entries will be shown.  Yummy!  My friends wont have to chew through all of my posts to see other recipes that I have blogged.  Saves time and frustration and makes your blog easier to navigate.