Indenting left margin without a left sidebar showing

I'm not quite sure if this is the right category to post in. I don't want a left sidebar, just a right one. I want the header to go from the left to right margin. But I want the posts to be slightly indented from the left.

How can I achieve this? I've tried all the options and have tried searching here, but can't come up with a way to do this.

Thanks for any help you can give me.