Well, I thought adopting a new template would maybe bring the sidebar back, but it just erased my color scheme. This one will do for now. I have posted a question to the Blogger tech-savvy folks, and hopefully someone will respond, "oh, ha ha ha, you non-tech-savvy blogger! The solution is so simple! ha ha ha!"
If any of you reader friends knows what I can do, please let me know.
I hate working with the HTML anyway (it's all computer-speak letters and numbers and slashes), and when I write a blog from my phone (which I just became capable of), they turn out wonky, so I tried to change it... and seemingly irrevocably erased the sidebar.