Head & menus

What I don’t quite understand in the use of this plugin is how headers/footers and menus work. If I invoke another theme for the blog section of my site, i.e. posts, does it mean I’ll have an entirely different look to the header and the menu bar?…styled by the alternative theme?

That would sound bonkers to me! Who would want a site where the whole appearance and look of the site suddenly changes…. fonts, sizes, colours, spacing, menu style and position etc. ?

I want my whole site to have the same header/menu style throughout – I just want to use another theme for the blog section to make it much more compact and simple (the blog section of my main theme is rather poor, but it’s ideal for the main pages).

I just don’t understand how you unify different themes under one style.