You can customise your WordPress site by changing its theme, to do this, hover over the Appearance option in the dashboard, and click on Themes.
A page showing all the themes you can choose from will show, hover over any of the themes and click Live Preview to see how it will look on your site, or click activate for it to become the theme you use
Any time you want to see how your site looks you can hover over your user name and click on Visit site.
You can customise your theme by hovering over appearance and clicking Customise.
Different themes come with different customisation options so have a play around!