Very useful dates functions for PostgreSQL.
The official documentation is here.
Getting the current date and time
SELECT NOW()
Getting the current day, no time
SELECT date_trunc('day', NOW())::date;
One hour later
SELECT (NOW() + interval '1 hour') AS one_hour_later;
One day later
SELECT NOW()+1
The day before
SELECT NOW()-1
For more complex calculations you can use intervals
For example:
SELECT (NOW() + interval '1 day') AS now_but_tomorrow;