Macros are pre-designed website code/features that you can drag (from the floating Macro bar) and drop on your page.
The macros available depend on the template and page you are editing but can include features such as checkboxes, text entry fields, date-picker widgets, load file field/buttons etc.
When EZGenerator presents you with a form of some kind (say Contact Request) there will be plenty of Macros to drop on the form to customize it to your needs.