Responsive web pages Made Easy
The easiest way to make a "responsive" website is to use a W3C template. That way everything has been worked out for you.
I did this for my Parish Council webste. The template that I used was the Portfolio Template. There is a link to the W3C site where the inspiration was taken. It now seems to be called the Nature Portfolio Template as W3C have updated their site.
I chose this template as it looked radically different from my own design and had a fixed side menu bar that overlays when in Mobile Phone resolution. Adapting it was still a lot of work but it was a place to learn.
Flexbox
There are many examples on the W3C site including the use of Flexbox, which won't work on some earlier browsers. I have an example here that looked at as a possible alternative.
Since starting this website I have made great strides in the field of responsive design.