WANTED: more details on "pg_databases" and/or "deleting template1 database"

The following documentation comment has been logged on the website:

Page: https://www.postgresql.org/docs/9.5/static/manage-ag-templatedbs.html
Description:

Hi !

(regarding article
https://www.postgresql.org/docs/current/static/manage-ag-templatedbs.html)

From the article it's not quite clear what is meant under "pg_databases" (is
it a table ? in which database ?) and also not clear how to "delete
template1 database". 

PS: The specific issue at hand is to modify default encodings for databases;
might be a good showcase example for the documentation.