How to Create Post Categories on Tumblrby Alan Sembera
Creating categories for your Tumblr posts makes it easier for followers to find topics that interest them, and can even bring in new readers who are searching based on a specific interest. The first step is to assign hash tags to each of your posts to identify the topic. Once you categorize the posts, you can create links in your Tumblr sidebar that take readers to another page containing all your posts about a certain topic.
Begin a new blog post as you would normally. To categorize an older post, click "Posts" on the dashboard, and then click the gear icon on the post and select "Edit."
Enter a category in the last field of the posting window, where you see the tag-shaped icon. You can make up any category -- just be consistent in your wording if you want several posts to appear in the same category. Tumblr suggests popular tags as you begin typing, and selecting one of these will help connect with new readers when they search Tumblr. Enter as many categories as you want.
Click "Post" or "Save Post" when you are finished creating or editing the post.
Create Category Links on Sidebar
Select your blog from the Tumblr dashboard and click "Customize."
Click "Add a Page" at the bottom of the settings pane.
Add one of your category tags to the end of the URL shown in the first field of the new window. For example, if you like reviewing movies and you used "movies" to tag all of your reviews, change the URL to "yourname.tumblr.com/movies".
Replace "Page Title" with a word or phrase that describes one of your categories. In the previous example, you may want to name the page "My Movie Reviews."
Add a description if you want to introduce your readers to the category at the top of the page.
Set the "Show a Link to This Page" switch to the on position.
Click "Save." Tumblr adds the page title to your blog's sidebar. You can click the title in the preview screen to see how the page looks, although you may have to give Tumblr a minute or two to update the link.
Click the back arrow in the Add a Page window. Click "Add a Page" to create another category page, or click "Exit" to return to the dashboard.