Log into the admin panel of your webiste. Click on Manage then Pages. You will see a list of pages. One of them is called Home.  Click on Home and add the content you want. If you want to add a picture, click on Add media ( Add an Image ) and upload your pictures.

If you want to change the design of your website, login to the admin panel and click on the Design (between Manage and Comments). Then click on Themes and select a theme. You can also change the color scheme by clicking on Header Image and Color and pick a new color scheme.