You can create tables and records in MySQL via SQL commands. For example:
CREATE TABLE pets (
id int,
species varchar(100),
name varchar(100)
);
INSERT INTO pets (species, name) VALUES ('dog', 'rover')
INSERT INTO pets (species, name) VALUES ('cat', 'fluffy')
In MySQL and most other databases, a set of commands like this can be generated from an existing table that will recreate it exactly. This set of commands can be saved in a file, and imported into a remote database. This is what DaWei means by describing the database with files.