What does First Section with Header do?

Adjusts the module height to account for the header when a section module is used at the top of the page

The Sec Hero module accounts for the header height and using the First Section with Header setting for Padding Top in Sec Modules will automatically adjust the height to avoid the header from overlapping the module content.

How to adjust the padding so the header doesn't overlap the module

From the section module settings, under Layout, choose First Section with Header: