Hi Sandy
These modules all live within the HTML of your email template.
There is specific Marketo syntax that can be added to the code that will determine what is one module and the controls a user that's using the template will have when editing that module.
More information on this can be found here: https://docs.marketo.com/display/public/DOCS/Email+Template+Syntax (Maybe start with the section titled 'Modules' towards the bottom of the page).
HTML for emails is very different to how you'd approach a website, so if you're not familiar with this an agency might be best (especially with the range of devices, email clients, mobile v desktop, dark mode, etc.). There are also some places online you can find pre-built Marketo templates (including the Marketo template library itself).
I hope this points you in the right direction!
John