How to set the correct featured image size on posts of diffetent categories?

I´m starting my first blog and I´m having troubles setting the correct image size on different categories postst. I have different sizes on different pages posts and I´m not able to set the featured image as it should be. Here you see the examples: (Not sure gow to upload images to this forum, god help me haha)

<img src="https://i.ibb.co/rcRF9Wf/Sin-t-tulo.jpg&quot; alt="<img src=”https://i.ibb.co/rcRF9Wf/Sin-t-tulo.jpg&#8221; alt=”Sin-t-tulo” border=”0″ />” />

<img src="<img src=”https://i.ibb.co/f82MJL9/1.jpg&#8221; alt=”1″ border=”0″ />” alt=”” />