Need very easy video tutorial to customize theme

After 12 days of videos, seminars, texts I still don’t know how to even begin customizing a theme, any theme that will serve as a simple store for Amazon Affiliate. I choose a theme, I see the page I am to begin say with Title, try to change just the color and not making any progress at all. What does it all mean, the terminology I have looked up in an internet glossary but return to the sample page and it stops there.
Would appreciate a very simple step by step video that the narrator is speaking like he is running a marathon.
Thank anyone for some feedback….