Getting a column comment in PostgreSql

Question

I have a table in my database and I hava added comments to each of the column in that table.

comment on column student_details.rollno is 'Roll No';

I have 6 such columns and I have added comments to each of the column in the same way.

I want to retrieve the comments using an sql query(PostgreSQL). I have checked few queries but they were complicated and I couldn't understand.

SELECT
cols.column_name,
(
    SELECT
        pg_catalog.col_description(c.oid, cols.ordinal_position::int)
    FROM
        pg_catalog.pg_class c
    WHERE
        c.oid = (SELECT ('"' || cols.table_name || '"')::regclass::oid)
        AND c.relname = cols.table_name
) AS column_comment
FROM
     information_schema.columns cols
WHERE
     cols.table_catalog    = 'your_database'
     AND cols.table_name   = 'your_table'

The above query worked for me but I don't know how. Can somebody explain this to me?