What you have to do is just to add a column in your table, and the name of the column should be 'category' (or what you want). This is an example code of the structure of "your" table:
CREATE TABLE clips(
id INT NOT NULL AUTO_INCREMENT,
PRIMARY KEY(id),
category VARCHAR(50) NOT NULL,
movie_name VARCHAR(30) NOT NULL,
movie_size VARCHAR(20) NOT NULL,
movie_length VARCHAR(20) NOT NULL
);
Then maybe you have a few clips, that belongs to the action category, and then you access them by pointing your browser to, for example movies.php?cat=action
Understand?