export PATH="export PATH=$PATH:/opt/lampp/bin". the export is a buildin command of bash, means export variables to be envirement variable.

mariadb -u root -p means, that you trying to connect to MariaDB shell with parameters:- -u parameter specified MariaDB user name. -u, --user=name User for login if not current user. In your case it's root user.-p, --password[=name] Password to use when connecting to server. If password is not given it's asked from the tty. You can type mariadb --help from the command line for more information about all available parameters.

The 'use databaseName' statement tells MariaDB to use the db_name database as the default (current) database for subsequent statements. The database remains the default until the end of the session or another USE statement is issued: The DATABASE () function ( SCHEMA () is a synonym) returns the default database.

SHOW DATABASES lists the databases on the MariaDB server host. SHOW SCHEMAS is a synonym for SHOW DATABASES.

SHOW TABLES lists the non-TEMPORARY tables, sequences and views in a given database.

DESC provides information about the columns in a table. It is a shortcut for SHOW COLUMNS FROM. These statements also display information for views.