Widgets can be added through Dashboard > Appearance > Widgets or in the Customizer. You will need to configure their options depending on what they do and how you would like them to appear.
The Home Left, Home Middle, Home Right, and Home Page Sections widgets only appear when using the Latest Posts Slider as your home page. The number of columns that appear will depend on the Homepage Layout you choose in Customizer > Theme Options > Homepage.
The Footer Left and Footer Right widgets appear in the footer on every page of your site. The Footer Left widget replaces the Resources links that appear by default, so this would be a good place for unit-specific resource links or other content you want to be accessible throughout the site.
Page and Post Widgets
Page Left Sidebar widgets appear in the left sidebar of all pages that use the Default page template.
Page Right Sidebar widgets appear in the right sidebar of all pages that use the Default or Right Sidebar, No Left Navigation page templates.
Post Sidebar widgets appear in the right sidebar of all posts.
If you wish to have page or post widgets display only on certain pages, you can request that the Dynamic Widgets plugin be activated on your site.