Please walk me through installing an exterior door in an unfinished basement

[Rhythmdvl]

Found after the edit window:
A couple details from Bilco’s FAQs:

Q. Why do I see light coming through Bilco door?
It is normal to see a small amount of daylight around the interior perimeter of the doors. The overlapping flanges are designed with a small gap to allow air flow to help reduce condensation on the underside of the doors. This gap will not affect the weather-tightness of the door.

Q. Is there a gasket or insulation kit available for Bilco basement doors?
Bilco does not offer a gasket or insulation kit for this product. Although the doors are designed to be weather-tight, Bilco recommends the use of an insulated vertical door at the bottom of your areaway for maximum energy efficiency.

I’d crawled their site before beginning all this to see if they sold a cover or some sort of insulation, but didn’t think to check in the FAQs.