How do I structure a simple Drupal 7 site/theme?
It sounds like most of the things that you need to do (i.e. creating and placing content on the site) are not related to a theme, but rather related to site building. Folks coming over from Wordpress are usually confused by the split between theming and site building in Drupal, it's very different from Wordpress.

I would strongly recommend reading Drupal's Site Structure Guide. Your homepage and "about" page will most likely be a combination of node content and blocks, while your "jobs" page will involve creating a custom content type and a Views page listing the nodes of that content type.

The majority of your work to set up the content of the site and it's output can happen before you even begin theming. Theming is usually a later step in site building and should be considered a very superficial aspect of building the site. There are few situations where you would need custom templates for each page or node type, most of the arrangement of content and even layout can be handled via the Drupal UI.

Once you complete the site build in Drupal and move on to theming, the Drupal Theming Guide will be your starting resource for learning how the Drupal theme layer works.