Super lost trying to make custom sidebar per header nav bar

I have spent all day working my way into a stupor trying to wrap my brain around this seemingly so easy concept. Still … it eludes me. If I think I have it working, I go into preview and it just doesn’t look at all like I wanted it set up as.

For instance: Welcome page

Call to Action Widget with Site Upgrades

Search Site

First Blog post – One Unique Double Helix

to the end of background Blog posts

The Way It Once Was: The Rest of the Story (5 posts in total)

About …

Image w/ Bio

Search Site

Preview Post/ Latest Blog entry

And so on …

Would you be able to walk me through the steps? I have to be missing something. This whole concept simply looks so easy. I have to be making it harder than what it really is.

Thank you,

Cecilia