Responsive Web Design Projects Review

To give you my background, I am totally new on HTML CSS and JS and just trying to apply what I am learning from FCC and other sources I got to read during my freetime.

After 3weeks long I just finished 3 out of 5 projects from Responsive Web Design.
I tried to achieve first the user story, and once I have met it, I proceed on implementing some basic designs that I understood from taking the 300hr certification on RWD.
I don’t know if I am doing the right thing, and I am implementing the codes correctly.
Was there a correct way that I need to follow writing these codes or I could just put those and as long as it achieve the design that I want and response to what I want it to do, that’s acceptable?
So I am hoping for some advise , If you could just cite some of the things that I need to correct on this stage of learning how to code. please do so. Thanks.

Here is the link on my codepen. please provide your feedback and I will be forever thankful to you,