If you already work productively with WebUntis, and would like to test WebUntis' "Substitution planning" in its beta phase, first create a playground (1:1 copy of your productive data). In this playground you can test the online substitution planning features without modifying your real data without any risk whatsoever.
Go to <Administration> | <Playground> and click on the <Create playground> button.
Go to: <Current> | <Duplicate WebUntis>.
After a short while, you are provided with a second WebUntis data set which you can access via <Open playground> and log in with your usual access data. Now, you can test all features of your school without modifying the current, productive data set.