Here you will learn how to display an image on a webpage and best practices when displaying images.
If you are not sure how to access the source code, you should go through the Getting Started documentation.
Before being able to insert the image it first must be uploaded to the CMS files. It is good practice to leave files in a folder to keep the filesystem organized, if you can't find an appropriate file to leave your image, go ahead and create one.
Once the image has been uploaded to the files, it's ready to be displayed on your page, follow the site-viz manual on uploading an image.