completely without a clue

I am not completely without a clue, but one wouldn’t guess that after looking at some of my web pages:
https://centrist.billbellavia.com
https://thomas.thewoodses.us
Yes, that is the default template you see there, with the very minor modifcation of changing the color.
I sure would like to know how to do more.
But my problem is that I can’t read the codes that make up a css layout. I’ve always done web design by means of Dreamweaver–what you see is what you get. (Usually. I find too often that other browsers on other operating systems display my sites so so wrong.)
So where can I go for a complete education on this?
Thanks,
Thomas