The icons on the right half are your WiFi signal, mobile radio signal, Bluetooth, etc.
The icons on the left are notifications.. just drag down on the top part of the screen and the notification shade will expand and show the apps that generated those notification icons (the icons at the very top of the shade are quick toggles). The first drag gives compact notifications, second drag gives them in their expanded mode. Many have actionable commands... Like replying in place for sms. In the shade, swiping left or right will dismiss, doing it halfway and you can mute them or change that app's notification settings.
Most everything is customizable... Just go poking around.