When To Use Quotes

I'm trying to understand when in SELECT statements should and should I
not use single quotes to filter my results. For example:

SELECT * FROM people
WHERE fname = 'James';

or

SELECT * FROM price
WHERE msrb
BETWEEN 50 AND 100;

Now is it correct to say that in PostgreSQL or ANSI SQL in general I
should use 'single quotes' when the condition is strictly a numerical
data type value and everything else should be inside 'single quotes'?