You can operate multiple devices at the same time by creating a group in the app. This is ideal for, for example:
A group of lamps in the living room
Several spotlights in the bathroom
Steps to create a group:
Go to My Family (bottom left in the app).
Select the first lamp you want to include in the group.
Open the menu (top right) and choose Create group.
Tick the devices that should be in the group and confirm.
Give the group a recognisable name, so you can easily find it later.