The Children tab is where you enter your children by first name. Each child has their own timer, which will count down their minutes across any devices they have.
The Devices tab is where all the devices you own are listed. The easiest way to add a device is to visit setup.screenlimit.net in a browser on the device, and it will direct you. Alternatively you can search your app store for ScreenLimit. Once added, you check the box next to each child that will be using each device.
The Apps tab is where you can set policies for different apps across the different platforms. Each platform has different capabilities to block, time or whitelist particular apps.
The Plans tab is where you can define Tasks and Schedules for groups of children. For example, a general family plan might have tasks of 'Do Homework' with a bonus of +5 minutes, available twice a day. Once set these bonus time buttons appear in the Children section in the drop-down beneath each child. The Schedule can be used to block/unblock or time/un-time children at different set times of the day.
If you haven't installed ScreenLimit yet, you can sign up here.