There are 2 options for linking to your images:
This option will present you with the option to add a url to your image
Drag and Drop
You can use this option to drage and drop / browse for local images.
Provide your Alternative text in this area
By default, Srcerer stack is set to display your image in 'Contain' mode which means that all of the image will be displayed.
If however you wish to use your image as a banner / Hero image, or you want to control the height of your image generally, then you can enable Cover mode.
Cover mode allows you to specify the image height (in px or % of browser height) for both mobile and desktop.