My Poem Categories section is actually a page. When you just do /tagged/poetry, that’s not really a page. It’s just a tag, a way of grouping your poems by a poetry tag.
If you want to create a separate page like my Poem Categories, you need to click "Customize" on your blog and then scroll down to “Pages," and then “Add a Page."
Then you need to name your page. So for example, if you want to have a page for posts about cats, you would do yoururl.com/cats. "Cats" is now the title of your page. Then you can just copy and paste the links to all your posts about cats into that page that you just named.
And you can keep adding more cat posts into that page by going back to “Customize" on your blog and then scrolling back down to “Pages" and clicking on “Edit" next to the Cats page.
Here Tumblr explains how to create and edit pages, so go there if you still have trouble after reading through my instructions.
I hope that helped! :)