To test your website, you'll first put some content on the Home page. Click on Page, click on the Home page and click on the green plus in the Content main box. Choose "Regular text element" (TYPO3 6.x) or "Text and media" (TYPO3 v7 and higher) and type some text in the Header and Text field. Save and close the element and you'll end up with something like this:
First result! Albeit only text. Open your website in a new browser window. If nothing appears, clear the TYPO3 cache and refresh the browser window with CTRL+F5. If still nothing appears, you might have missed a step. But you should see the text you've just added to the home page! When you look at the source code of the Home page, you'll see that the template is in place and the content_main div is filled with your content. The content_menu part is still empty; you will use some typoscript later to add the menu.
Right now this page can hardly be called a website. Therefore, you need to add a layout and a CSS style sheet. Remember; if your website only has 1 template, you can add the entire website layout to that template as well. In that case, your template is your website layout. However, in this example you will use a separate layout, which will be using 3 different templates for the content part.