Images are a core part of emails, and can be placed easily into your build.
Once you have a Column in your email, you'll be able to use the blue plus icon to add an image, demonstrated below.
Once your image placeholder is there, follow the instruction and double click it, to bring up the images folders. Folders can be created to hold and sort images (.jpg, .png, .gif). Once you've uploaded an image, it will sit in the folder ready to be used, and can be placed into your email using the "Insert Selected" button shown below.
You'll then see your image in your email, and you can use the Properties Panel to give your image a link, add 'alt text', resize it and more. Read all about the Properties Panel here.