Adding a banner and picture in sidebar with transparent background

I just created a blog. I know absolutely nothing about HTML or CSS. I am in a little over my head and I am having a lot of trouble customizing my blog. Right now I am using a Lightword theme. But I really just need to find a theme that is good for beginners.

I want to add a banner in the header and a picture in the sidebar both with a transparent background. I have no idea how to do this. Any help would be greatly appreciated.

Here is a link to my “site”: fangbot.com