To place a reservation in a box, you must first create a reservation. For more information on how to create a reservation, see How do I create a reservation? of How do I create a reservation for the Virtual Vending Machine?
A reservation can be placed in a box at "Overview", "Reservations" or at "Lockers". For more information about the other pages, see:

At the top you will see an overview with the current locker content.
When you scroll down in this overview, you will arrive at an overview of reservations. Click on the reservation you wish to place in a box. In the detail of the reservation, click on "Reserve box".

If you choose multiple boxes, the customer will only receive 1 code to open the different boxes. When entering the code, the different boxes open simultaneously.
You can switch between lockers via the dropdown menu.
Click on "Reserve box" to assign a box.

The customer will automatically receive his code x hours before the pick up hour. You can determine this time interval yourself in the settings.