Static theme?

Hi. So I’m creating a theme for my friend. She has a separate blog page and a few content pages. I’m curious how do I incorporate this into the theme? As in, how can I create separate templates to include blog posts & her specific content so that when she downloads it, it will work without trouble.

Just in general, I don’t really understand how the page template things work and how to include and prepare them so when the theme is downloaded, their content will just fit right in. I’d really appreciate some help.