When first creating your Google Site, there will be an options pane to the right of the screen. The 'Insert' section will allow you to manipulate the page that has been created by adding text boxes, images, embedding links and uploading items from your Google Drive.
There are a number of options in this section which allow you to change the layout of the page and with these preset layouts, you can change how the page is shown once it has been published.
These are the four basic options available in the 'Insert' section. Each one will allow you to put a specific bit of content on the site.
Text Box will allow you to add written content to the page
Images allow you to upload images from your desktop or select certain images from the internet or already available images from Google.
Embed allows you to insert a URL into the page, this could be a YouTube video or a link to a PDF.
Drive will let you upload any document available from your Google Drive. You can change settings so items which are in your personal drive can be viewed by different people.
The first section on the preset layout allows you to have an image/video to one side with a section of text to the right of the page.
The second preset will allow you to add 2 images with 2 description boxes at the bottom.
The third preset will allow you to add three separate media such as images/videos in one section.
The fourth preset will give three media sections and three descriptions at the bottom.
Reminder: These are only presets and you can play around with these and try different ways to present your content.