I am long time - old time - programmer trying to learn new skills on Codecademy. I have completed the HTML& CSS course on the way to finishing the Full Stack Developer course in 2017.
Fist of all, very well done You can be proud of yourself
how large is the image? maybe compress it? It seems pretty big, as such it takes a lot of time to load
the codecademy course does not cover col-xs-* and col-sm-*, onlycol-md-*`, but knowing the other cols for smaller screen is really nice, you can read about it here:
The grid system will help, but you should then look into the media querys, in the beginning, focus on max-width and min-width, this allow different css code for different screen sizes