Categories in WordPress are the topics you use to organize your posts. If you have sub domains then the categories in each sub domain would be the sub-niche topics for the sub domain main keyword.
So if your niche is ‘golden retrievers’ you may have a sub domains: ‘nutrition’, ‘grooming’, ‘training’ and ‘health’. You may then split down your sub domain ‘nutrition’ into some categories: puppy nutrition, adult nutrition, senior nutrition, special diets and so on.
If you are not using sub domains – at least yet – then your categories will be the topics that could become sub domains later. So in the example above - you may start with categories: ‘nutrition’, ‘grooming’, ‘training’ and ‘health’.
In WPM you can create sub-categories so ‘nutrition’ would then be the parent category of ‘puppy nutrition’, ‘adult nutrition’ and all the rest. The important thing is that your categories make sense based on the research you did when setting up the site.
TIP: make sure the keyword for your topic or sub-niche is included in your category name. Simple is better in this respect. If you have a category about puppy nutrition because your research told you that was a good key word then call it ‘puppy nutrition’. Easy really.
Does this stuff make any difference? Well, you probably won’t be surprised to learn that categories matter.
The categories you create, what you call them, and how you assign posts to them matters very much.
It's important for two reasons:
As an example of this last point, consider these search engine results:
“Passive smoking causes skin damage” is the #4 result out of 1.09 million pages from a search in Google on “skin and smoking reverse”.
What is interesting here is that Google has merged two posts in the same category to create the result.
“Smoking ages skin – spaniel eared breasts anyone” is a separate post which the spider pushes together as one result because it is in the same category. So when it searches for relevant keywords it uses that post as well.
“Smoking and Skin Aging” on the other hand is a page. Google uses the relevant key words but it is being treated as a separate result.
The more you post in a topic, the more you offer your visitor and the more you are rewarded in Google with higher rankings on all sorts of queries related to your keywords.
In a nutshell: VISITOR OPTIMIZATION = SEARCH ENGINE OPTIMIZATION
Because categories are so important, WPM has a whole section for setting them up properly within your Admin. Go to Manage/Categories, and set up your categories and sub-categories as you want.
Use the “description” box to enter a phrase that will show up when the visitor’s cursor hovers over the category name.
When you type a new post in the “write post” screen, click to select the category for your post. Usually it's best to select just one category. You may want to check more than one category for some posts, but try to avoid doing this for too many as the categories will become meaningless.
Click on the icon in the editing area to create a break after the first or second paragraph. Now when the visitor clicks on the category name each post will show with the relevant portion and the ‘read more’ text.
You'll need to monitor your categories on a regular basis to make sure the organization still makes sense as the number of your posts grows.
Remember that your categories list will help your visitors navigate your site better.