Creating categories within blog on 7.1

Site URL: https://www.mayamukhopadhaya.com/portfolio-blog-style

I have a mix of different types of work I would like to showcase- product management, design research, strategy and workshop facilitation.

Since it is a mix of different types of work, I would like to use "categories" to help the audience navigate which 'posts' are relevant to them. For example, someone interested in product management experience could click on posts categorized as product management. 

But I can't figure out how/where to add categories to posts in order to achieve that. 

PW to site url: mayam

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thank you!