WordPress is a “Theme” based system. The “Theme” you choose dictates the basic layout and appearance of the website. Once you’ve chosen a theme, you can customize it by changing the colour scheme, background images, what’s in the menus and sidebars, and so on. The WordPress documentation for Themes is at: http://codex.wordpress.org/Themes.
In the administration menu, you change themes and customize the current theme with the Appearance menu:
To change theme, pick “Themes”:
This will take you to the screen that allows you to pick a theme for the website:
By default, you start with just a few themes to choose from, but there are hundreds more that you can download with just a click of the mouse and try out. To browse and download themes, click on “Add New Theme”
Once you have a theme that’s structured the way you like it, you can customize it, changing colours and so on. To do so, click on the “Customize” menu item in the Appearance menu:
This will take you to a screen where you can customize the theme’s appearance, changing colours, background images, menus, what’s in the header and sidebar, etc.
This site is running on WordPress. There are lots of online resources for it. The first place I usually go to figure out how to do things with Wordpress is its main documentation page: codex.wordpress.org.