Some of the homework I’ve been setting myself over summer has involved taking an existing website and completely re-building it in my own code, only looking at the source when I’m really stuck. I find this is a great way for someone who has no experience designing for the web to get practising the basic skills of front-end development; as well as this I think that copying from good examples gives me some insight into the world of screen design before I learn more of the design side in my second year of university.
For now my sites will not be built using frameworks, as I believe a robust understanding of standalone HTML / CSS will be more useful to me for the time being than frameworks. The very primitive method I used was to contain elements that needed to be responsive in a div, then adjust the widths of those elements according to the screen size. In this case it pretty much means changing everything to 100% when the window is at lower widths. The main responsive elements are the navbar (with it’s heading), the four information box elements (sized at 25%, 50% and 100% for each window width) and the large blue section at the bottom.