The Availability tab in the planning tool allows the planner to get an overview of all of their resources' availabilities for each time slot. The number indicated in each cell determines the number of resources available for this time slot with regards to the absences they have input.
Hence, it is relevant to glance over the period through this tab before starting the group planning to avoid problems due to the entry of too many absences.
When clicking on a specific cell, it is also possible to see the list of available (in black) VS non-available (in red) resources.