In the United States, you generally have your specific apartment number as part of your address, like so:
John Smith
123 W Main St #456
Pleasantville, PA 12345
The mailman will then find the mailbox labeled '#456' at the apartment building at 123 W Main St.
However in Germany, you would instead write:
John Smith
Mainstr. 123
50505 Pleasantville
And the mailman will find the mailbox labelled 'Smith' at the apartment building at Mainstr. 123. So effectively, your last name becomes critical to your mail being delivered, and your address is shared amongst everyone else in your apartment building.
Where the actual door to your apartment is remains unknown to the mailman, post office, and person sending you mail.
John Smith 123 W Main St #456 Pleasantville, PA 12345
The mailman will then find the mailbox labeled '#456' at the apartment building at 123 W Main St.
However in Germany, you would instead write:
John Smith Mainstr. 123 50505 Pleasantville
And the mailman will find the mailbox labelled 'Smith' at the apartment building at Mainstr. 123. So effectively, your last name becomes critical to your mail being delivered, and your address is shared amongst everyone else in your apartment building.
Where the actual door to your apartment is remains unknown to the mailman, post office, and person sending you mail.