What do I need to do to adapt my Web site to mobile devices?

I have a Web site for high school level math. It is mostly text with some illustrations. You can see it here I used a freeware tool for creating the Web pages.

Google’s Web site rankings take mobile friendliness into account and they have an online site evaluater. My site did not do very well. I like talking about math, but do not care particularly for the intricacies of Web page design. Are there some simple basic things that I can do to improve my site’s mobility, like settings for font and image size? Does DreamWeaver or other commercial applications optimize for mobile devices?