Until you’re very familiar with WordPress it can be difficult to find where to modify some of the features. It’s easy enough to add a new category for your posts right from the Write Post page. Over there on the right just type a new category in the box under Categories and click Add. Or add several categories at one time by separating them with commas.
The default post category can be changed from “uncategorized” to your choice of category by going to Options/Writing.
Writing options shows the default post category of “uncategorized.”
At the default post category dropdown box, pick one you like and click on Update Options to make it so.
Add a new category by going to Manage/Categories. The trick here is that you can delete the uncategorized category after another category is selected as the default.
Manage categories for WordPress blogs.
You picked the category you want as your default in the Options/Writing screen, or here you can click on add new to add more categories for your blog. Then, in the far right column, delete the uncategorized category.
A warning box pops up to alert you that you’re going to delete a category and that the posts that were assigned to the category to be deleted will now be assigned to the new default category.
Alert box shows you’re about to delete a category.
Click OK to make it so. You’ve gotten rid of the uncategorized category.