Check out example codes for "select current_timestamp - interval '3 days';". It will help you in understanding the concepts better.

Code Example 1

--yesterday
SELECT NOW() - INTERVAL '1 DAY';

--Unrelated to the question, but PostgreSQL also supports some shortcuts:
SELECT 'yesterday'::TIMESTAMP, 'tomorrow'::TIMESTAMP, 'allballs'::TIME;

Code Example 2

SELECT current_timestamp - interval "3 days";
-- 2020-06-24 08:25:31.759993 America/Los_Angeles

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