How does one add a directory to a web host through code?

I am working on a web application on a web host server. The server is an Apache server running MySQL and I am using PHP. My server is on 000webost.com . I am trying t开发者_开发百科o code so that a new directory is added to the server every time a new test is created in my application. How would I do this?

you can create a new directory w/ PHP's mkdir('mydir', 0777);

PHP mkdir