Appearance won't update

HI there,

I’m brand new to this site building business. I’m working in dashboard trying to customize the default theme. I’ve managed to change the color and header image (which took several attempts to update) and now I’m trying to add widgets and such to the side bar. I apply, save, and absolutely nothing happens. At first, the header wouldn’t change in Firefox but it did in Chrome. Then mysteriously, it changed in Firefox the next day. I’ve read through the start up articles. I realize having experience with code and such is a plus but I was under the impression it wasn’t necessary. Am I wrong? Am I in over my head choosing wp.org vs wp.com? Isn’t it possible to make basic changes without changing code? Thanks!

here is my site https://www.gazebotreevintage.com