GIVE ANSWERS - Deutsch

"In dem" (=im) is the Dativ Form for maskulinum and neutrum - "der" and "das". In this case its used to explain where is something. Examples:
In dem Haus (in the house)
In dem Auto (in the car)
Im Leben (in life)
In dem Krankenhaus (in the hospital)
Etc.

"In den" is the Dativ form of all plural words. Its also used to describe the position of an object.
Examples:
In den Häuser (in the houses)
In den Autos (in the cars)
Etc.