Hi Maliq, Take time to choose a theme because the themes operate in thier own different ways.
But you will work it out one way or the other as long as your customers can navigate easily you will be fine.
I didn't answer because some others already have.
Best wishes,
Melvin.

After you add your categories under Post, you go to Appearance - Widgets, and you can add Categories under your Content Sidebar. This will display your categories. This is what I am also currently working on, so I believe this is correct. Hope this helps.
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This is a tutorial that can help: Creating A Category Page