As soon as one teacher from your school has opened English Every Day for the students, they can do the Level Test in their personal user account. If they don't have one yet they can create one here.
In their user account they just need to click on 'Events', then on 'Level Test'. After that they just need to choose their level and off they go. It's best to do the test on a desktop computer.
The Level Test can be done at any time, at home or at school. It doesn't need to be taken by everyone at the same time.
You'll see the students' results in your teacher user account the day after they've taken it.