How does postgres drop all tables in schema through command?

You want to use the CASCADE option of postgres DROP all tables SCHEMA. From the documentation:

CASCADE - Automatically drop objects (tables, functions, etc.) that are contained in the schema, and in turn all objects that depend on those objects

BE CAREFUL - emphasis above mine.
Obviously you'll need to recreate the schema afterwards.
To just drop all tables in the current schema, you can use this script:
DO $$ DECLARE
    tabname RECORD;
BEGIN
    FOR tab name IN (SELECT tablename 
                    FROM pg_tables 
                    WHERE schemaname = current_schema()) 
LOOP
    EXECUTE 'DROP TABLE IF EXISTS ' || quote_ident(tabname.tablename) || ' CASCADE';
END LOOP;
END $$;
Change WHERE schemaname = current_schema() if you want to drop all of the tables in a different schema.