This is how you do it
Open Planner in the browser and sign in with your Microsoft 365 account. Your account must have access to the solution.
Select the date and the meeting rooms you want to work with. Use size, location and equipment to find a suitable, available room.
Create the meeting, fill in participants and title, and send the invitation. Check that the room has accepted the reservation.
Use the overview to change the room or time. Your rights determine whether you can update directly or have to send a request to the organizer.
Add meals from the menu and save the order before the applicable deadline.