Header doesn't adjust dynamically

Hi All,
I am a newbie here and this is my second post.
First of, I have no WP knowledge or web programming experience.

So, I try to adjust my browser to different widths but my header doesn’t adjust with it. Is this what people refer to as not being “responsive”?

I have read other post and some of them skip steps, and or aren’t detailed enough.

What I have done.
I have created a child theme and child theme folder. Currently, the child theme folder contains the following:
inc folder
style.css
header.php
Also my header img is .jpg format. I also uploaded a .png version.

I also have the “custom css” plugin if this information helps in helping me resolve my issue.