Resonsive web design using viewport

What are you most proud of, and what would you do differently next time?

I am a beginner in web development. I am most pround on myself that i managed to do this myself without any googling for answer.

What challenges did you encounter, and how did you overcome them?

I face a lot of challenges such as not flex not working i overcome from this by just removing and then checking the css selector and i found out that i just missed a colon at the end.

What specific areas of your project would you like help with?

i need help if someone can tell me how to make a responsive site i know about viewport meta tag but i dont know what is the meaning of viewport height (vh) and viewport width (vw) units and ,where to use it ??