How can I insulate the entry door?

Answer 1

there are several types of insulating you can do, depending on which is best for your application:
Self-adhesive foam strip
Self-adhesive rubber strip, tougher - will last longer than foam strips
Brush strips - particularly useful on surfaces moving against each other, such as patio doors and sash windows.
Silicone rubber sealant - useful when filling gaps of an uneven, irregular gaps.
Sprung strip - more durable than foam or rubber strips, and suitable for uneven gaps.
Flexible tube

Answer 2

Household? You can pickup foam tape to seal the door where it closes. Home Depot carries this stuff.