How to access a second database

I am trying to access a table from another database. I have the permissions
to create under my own login. I have performed the following so far:
sherman(at)sql-dev: createdb sandbox01
sherman(at)sql-dev:~$ createdb sandbox02.
After logging into sandbox02 I performed the following: sandbox02=# CREATE
TABLE last_names(last_name TEXT);
sandbox02=# INSERT INTO last_names VALUES(willden);

Now I think I want to use a foreign key in sandbox01. Is the following how
it works after logging into sandbox01?

sandbox01=# CREATE TABLE first_and_last(first_name TEXT, last_name FOREIGN
KEY last_name REFERENCES sandbox02(last_names(last_name))

and then sandbox01=# INSERT INTO first_and_last(sherman, willden);

Thank you;

Sherman