Would like to use the child

I installed and activated the child and things changed a lot. I was able to make text color changes easily. The widgets I had installed on the blog page disappeared. I changed the featured photo on the header and it was than that I realized that I need to make a lot of changes to include a lot that I had done in the parent. One thing I noticed is that an Adsense template appeared on all pages. I don’t know how to get rid of it or change it. Is there a tutorial on YouTube?