Filter articles by category

Hello,

(My site is a test site.)
What I am trying to do:
I have 3 categories of articles: Video Games, Cinema and Computer.
I would like that in my filter bar, I can have my categories, and if I click for example on cinema, to display only the articles which belong to cinema.

Only Flow-Flow has created me a single “wordpress” button bringing together all the articles, regardless of category.

Help me please, thank you for your response.

The page I need help with: [log in to see the link]