A demo lesson is your chance to get to know your tutor. Just like any lesson, it is paid. However, after a demo lesson, you can decide whether you want to continue studying with the tutor you've selected.
During your demo lesson, you'll get to know your tutor, discuss your learning goals and develop a learning plan to achieve them. Normally, you'll perform regular class activities that will help your tutor to evaluate your level of knowledge and allow you to get to know the tutor's teaching style.